diff --git a/CMakeLists.txt b/CMakeLists.txt
index 2a23941..c1ad691 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -47,7 +47,7 @@ set(HEADER_FILES
     id3/id3v2tag.h
     ivf/ivfframe.h
     ivf/ivfstream.h
-    language.h
+    localehelper.h
     localeawarestring.h
     margin.h
     matroska/ebmlelement.h
@@ -122,7 +122,7 @@ set(SRC_FILES
     id3/id3v2tag.cpp
     ivf/ivfframe.cpp
     ivf/ivfstream.cpp
-    language.cpp
+    localehelper.cpp
     localeawarestring.cpp
     matroska/ebmlelement.cpp
     matroska/matroskaattachment.cpp
diff --git a/abstracttrack.cpp b/abstracttrack.cpp
index 23aaf8f..37d3999 100644
--- a/abstracttrack.cpp
+++ b/abstracttrack.cpp
@@ -1,6 +1,5 @@
 #include "./abstracttrack.h"
 #include "./exceptions.h"
-#include "./language.h"
 #include "./mediaformat.h"
 
 #include "./mp4/mp4ids.h"
@@ -130,8 +129,8 @@ string AbstractTrack::label() const
     if (!name().empty()) {
         ss << ", name: \"" << name() << "\"";
     }
-    if (isLanguageDefined(language())) {
-        ss << ", language: " << languageNameFromIsoWithFallback(language()) << "";
+    if (const auto &language = locale().fullOrSomeAbbreviatedName(); !language.empty()) {
+        ss << ", language: " << language << "";
     }
     return ss.str();
 }
@@ -173,13 +172,13 @@ string AbstractTrack::makeDescription(bool verbose) const
     case MediaType::Audio:
     case MediaType::Text:
         if (channelCount()) {
-            if (!language().empty() && language() != "und") {
-                return argsToString(formatName, '-', channelCount(), "ch-", language());
+            if (const auto &localeName = locale().someAbbreviatedName(); !localeName.empty()) {
+                return argsToString(formatName, '-', channelCount(), "ch-", localeName);
             } else {
                 return argsToString(formatName, '-', channelCount(), 'c', 'h');
             }
-        } else if (!language().empty() && language() != "und") {
-            additionalInfoRef = language().data();
+        } else if (const auto &localeName = locale().someAbbreviatedName(); !localeName.empty()) {
+            additionalInfoRef = localeName.data();
         }
         break;
     default:;
diff --git a/abstracttrack.h b/abstracttrack.h
index b461d14..13fe524 100644
--- a/abstracttrack.h
+++ b/abstracttrack.h
@@ -3,6 +3,7 @@
 
 #include "./aspectratio.h"
 #include "./diagnostics.h"
+#include "./localehelper.h"
 #include "./margin.h"
 #include "./mediaformat.h"
 #include "./size.h"
@@ -95,8 +96,8 @@ public:
     double maxBitrate() const;
     const CppUtilities::DateTime &creationTime() const;
     const CppUtilities::DateTime &modificationTime() const;
-    const std::string &language() const;
-    void setLanguage(const std::string &language);
+    const Locale &locale() const;
+    void setLocale(const Locale &locale);
     std::uint32_t samplingFrequency() const;
     std::uint32_t extensionSamplingFrequency() const;
     std::uint16_t bitsPerSample() const;
@@ -160,7 +161,7 @@ protected:
     double m_maxBitrate;
     CppUtilities::DateTime m_creationTime;
     CppUtilities::DateTime m_modificationTime;
-    std::string m_language;
+    Locale m_locale;
     std::uint32_t m_samplingFrequency;
     std::uint32_t m_extensionSamplingFrequency;
     std::uint16_t m_bitsPerSample;
@@ -435,22 +436,22 @@ inline const CppUtilities::DateTime &AbstractTrack::modificationTime() const
 }
 
 /*!
- * \brief Returns the language of the track if known; otherwise returns an empty string.
+ * \brief Returns the locale of the track if known; otherwise returns an empty locale.
  *
- * The format of the language denotation depends on the particular implementation.
+ * The format of the locale depends on the particular format/implementation.
  */
-inline const std::string &AbstractTrack::language() const
+inline const Locale &AbstractTrack::locale() const
 {
-    return m_language;
+    return m_locale;
 }
 
 /*!
- * \brief Sets the language of the track.
- * \remarks Whether the new value is applied when saving changes depends on the implementation.
+ * \brief Sets the locale of the track.
+ * \remarks Whether the new value is applied when saving changes depends on the format/implementation.
  */
-inline void AbstractTrack::setLanguage(const std::string &language)
+inline void AbstractTrack::setLocale(const Locale &locale)
 {
-    m_language = language;
+    m_locale = locale;
 }
 
 /*!
@@ -621,11 +622,11 @@ inline std::uint32_t AbstractTrack::timeScale() const
 }
 
 /*!
- * \brief Returns true if the track is denoted as enabled; otherwise returns false.
+ * \brief Returns true if the track is marked as enabled; otherwise returns false.
  */
 inline bool AbstractTrack::isEnabled() const
 {
-    return m_enabled;
+    return m_flags & TrackFlags::Enabled;
 }
 
 /*!
@@ -634,15 +635,15 @@ inline bool AbstractTrack::isEnabled() const
  */
 inline void AbstractTrack::setEnabled(bool enabled)
 {
-    m_enabled = enabled;
+    CppUtilities::modFlagEnum(m_flags, TrackFlags::Enabled, enabled);
 }
 
 /*!
- * \brief Returns true if the track is denoted as default; otherwise returns false.
+ * \brief Returns true if the track is marked as default; otherwise returns false.
  */
 inline bool AbstractTrack::isDefault() const
 {
-    return m_default;
+    return m_flags & TrackFlags::Default;
 }
 
 /*!
@@ -651,15 +652,15 @@ inline bool AbstractTrack::isDefault() const
  */
 inline void AbstractTrack::setDefault(bool isDefault)
 {
-    m_default = isDefault;
+    CppUtilities::modFlagEnum(m_flags, TrackFlags::Default, isDefault);
 }
 
 /*!
- * \brief Returns true if the track is denoted as forced; otherwise returns false.
+ * \brief Returns true if the track is marked as forced; otherwise returns false.
  */
 inline bool AbstractTrack::isForced() const
 {
-    return m_forced;
+    return m_flags & TrackFlags::Forced;
 }
 
 /*!
@@ -668,7 +669,7 @@ inline bool AbstractTrack::isForced() const
  */
 inline void AbstractTrack::setForced(bool forced)
 {
-    m_forced = forced;
+    CppUtilities::modFlagEnum(m_flags, TrackFlags::Forced, forced);
 }
 
 /*!
@@ -676,15 +677,15 @@ inline void AbstractTrack::setForced(bool forced)
  */
 inline bool AbstractTrack::hasLacing() const
 {
-    return m_lacing;
+    return m_flags & TrackFlags::Lacing;
 }
 
 /*!
- * \brief Returns true if the track is denoted as encrypted; otherwise returns false.
+ * \brief Returns true if the track is marked as encrypted; otherwise returns false.
  */
 inline bool AbstractTrack::isEncrypted() const
 {
-    return m_encrypted;
+    return m_flags & TrackFlags::Encrypted;
 }
 
 /*!
@@ -708,7 +709,7 @@ inline const Margin &AbstractTrack::cropping() const
  */
 inline bool AbstractTrack::isHeaderValid() const
 {
-    return m_headerValid;
+    return m_flags & TrackFlags::HeaderValid;
 }
 
 } // namespace TagParser
diff --git a/id3/id3v2frame.cpp b/id3/id3v2frame.cpp
index 9f85d5e..4ef5396 100644
--- a/id3/id3v2frame.cpp
+++ b/id3/id3v2frame.cpp
@@ -981,7 +981,7 @@ void Id3v2Frame::parseComment(const char *buffer, std::size_t dataSize, TagValue
     }
     TagTextEncoding dataEncoding = parseTextEncodingByte(static_cast<std::uint8_t>(*buffer), diag);
     if (*(++buffer)) {
-        tagValue.setLanguage(string(buffer, 3));
+        tagValue.setLocale(Locale(std::string(buffer, 3), LocaleFormat::ISO_639_2_B)); // does standard say whether T or B?
     }
     auto substr = parseSubstring(buffer += 3, dataSize -= 4, dataEncoding, true, diag);
     tagValue.setDescription(string(get<0>(substr), get<1>(substr)), dataEncoding);
@@ -1163,8 +1163,8 @@ void Id3v2Frame::makeComment(unique_ptr<char[]> &buffer, std::uint32_t &bufferSi
         diag.emplace_back(DiagLevel::Critical, "Data encoding and description encoding aren't equal.", context);
         throw InvalidDataException();
     }
-    const string &lng = comment.language();
-    if (lng.length() > 3) {
+    const string &language = comment.locale().abbreviatedName(LocaleFormat::ISO_639_2_B, LocaleFormat::ISO_639_2_T, LocaleFormat::Unknown);
+    if (language.length() > 3) {
         diag.emplace_back(DiagLevel::Critical, "The language must be 3 bytes long (ISO-639-2).", context);
         throw InvalidDataException();
     }
@@ -1198,7 +1198,7 @@ void Id3v2Frame::makeComment(unique_ptr<char[]> &buffer, std::uint32_t &bufferSi
 
     // write language
     for (unsigned int i = 0; i < 3; ++i) {
-        *(++offset) = (lng.length() > i) ? lng[i] : 0x00;
+        *(++offset) = (language.length() > i) ? language[i] : 0x00;
     }
 
     // write description
diff --git a/language.cpp b/language.cpp
deleted file mode 100644
index 24fea30..0000000
--- a/language.cpp
+++ /dev/null
@@ -1,44 +0,0 @@
-#include "./language.h"
-
-#include <unordered_map>
-
-namespace TagParser {
-
-/// \cond
-static const auto &languageMapping()
-{
-#include "resources/languages.h"
-    return languages;
-}
-/// \endcond
-
-/*!
- * \brief Returns the language name for the specified ISO-639-2 code (bibliographic, 639-2/B).
- * \remarks If \a isoCode is unknown an empty string is returned.
- */
-const std::string &languageNameFromIso(const std::string &isoCode)
-{
-    const auto &mapping = languageMapping();
-    const auto i = mapping.find(isoCode);
-    if (i == mapping.cend()) {
-        static const std::string empty;
-        return empty;
-    }
-    return i->second;
-}
-
-/*!
- * \brief Returns the language name for the specified ISO-639-2 code (bibliographic, 639-2/B).
- * \remarks If \a isoCode is unknown the \a isoCode itself is returned.
- */
-const std::string &languageNameFromIsoWithFallback(const std::string &isoCode)
-{
-    const auto &mapping = languageMapping();
-    const auto i = mapping.find(isoCode);
-    if (i == mapping.cend()) {
-        return isoCode;
-    }
-    return i->second;
-}
-
-} // namespace TagParser
diff --git a/language.h b/language.h
deleted file mode 100644
index 07569e2..0000000
--- a/language.h
+++ /dev/null
@@ -1,26 +0,0 @@
-#ifndef TAG_PARSER_LANGUAGE_H
-#define TAG_PARSER_LANGUAGE_H
-
-#include "./global.h"
-
-#include <c++utilities/conversion/stringbuilder.h>
-
-#include <cstdint>
-#include <string>
-
-namespace TagParser {
-
-/*!
- * \brief Returns whether \a languageSpecification is not empty or undefined.
- */
-inline bool isLanguageDefined(const std::string &languageSpecification)
-{
-    return !languageSpecification.empty() && languageSpecification != "und";
-}
-
-TAG_PARSER_EXPORT const std::string &languageNameFromIso(const std::string &isoCode);
-TAG_PARSER_EXPORT const std::string &languageNameFromIsoWithFallback(const std::string &isoCode);
-
-} // namespace TagParser
-
-#endif // TAG_PARSER_LANGUAGE_H
diff --git a/localeawarestring.h b/localeawarestring.h
index 3f23f0d..09e151d 100644
--- a/localeawarestring.h
+++ b/localeawarestring.h
@@ -1,7 +1,7 @@
 #ifndef TAG_PARSER_LOCALEAWARESTRING_H
 #define TAG_PARSER_LOCALEAWARESTRING_H
 
-#include "./global.h"
+#include "./localehelper.h"
 
 #include <string>
 #include <vector>
@@ -17,14 +17,11 @@ public:
     explicit LocaleAwareString(std::string &&value);
     ~LocaleAwareString();
 
-    const std::vector<std::string> &languages() const;
-    std::vector<std::string> &languages();
-    const std::vector<std::string> &countries() const;
-    std::vector<std::string> &countries();
+    const Locale &locale() const;
+    Locale &locale();
 
 private:
-    std::vector<std::string> m_languages;
-    std::vector<std::string> m_countries;
+    Locale m_locale;
 };
 
 /*!
@@ -51,35 +48,19 @@ inline LocaleAwareString::~LocaleAwareString()
 }
 
 /*!
- * \brief Returns associated languages.
+ * \brief Returns the associated locale.
  */
-inline const std::vector<std::string> &LocaleAwareString::languages() const
+inline const Locale &LocaleAwareString::locale() const
 {
-    return m_languages;
+    return m_locale;
 }
 
 /*!
- * \brief Returns associated languages.
+ * \brief Returns the associated locale.
  */
-inline std::vector<std::string> &LocaleAwareString::languages()
+inline Locale &LocaleAwareString::locale()
 {
-    return m_languages;
-}
-
-/*!
- * \brief Returns associated countries.
- */
-inline const std::vector<std::string> &LocaleAwareString::countries() const
-{
-    return m_countries;
-}
-
-/*!
- * \brief Returns associated countries.
- */
-inline std::vector<std::string> &LocaleAwareString::countries()
-{
-    return m_countries;
+    return m_locale;
 }
 
 } // namespace TagParser
diff --git a/localehelper.cpp b/localehelper.cpp
new file mode 100644
index 0000000..16cd04e
--- /dev/null
+++ b/localehelper.cpp
@@ -0,0 +1,143 @@
+#include "./localehelper.h"
+
+#include <c++utilities/conversion/stringconversion.h>
+
+#include <unordered_map>
+
+using namespace std::literals;
+
+namespace TagParser {
+
+/// \cond
+static const auto &languageMapping()
+{
+#include "resources/languages.h"
+    return languages;
+}
+/// \endcond
+
+/*!
+ * \brief Returns the language name for the specified ISO-639-2 code (bibliographic, 639-2/B).
+ * \remarks If \a isoCode is unknown an empty string is returned.
+ */
+const std::string &languageNameFromIso(const std::string &isoCode)
+{
+    const auto &mapping = languageMapping();
+    const auto i = mapping.find(isoCode);
+    if (i == mapping.cend()) {
+        static const std::string empty;
+        return empty;
+    }
+    return i->second;
+}
+
+/*!
+ * \brief Returns the language name for the specified ISO-639-2 code (bibliographic, 639-2/B).
+ * \remarks If \a isoCode is unknown the \a isoCode itself is returned.
+ */
+const std::string &languageNameFromIsoWithFallback(const std::string &isoCode)
+{
+    const auto &mapping = languageMapping();
+    const auto i = mapping.find(isoCode);
+    if (i == mapping.cend()) {
+        return isoCode;
+    }
+    return i->second;
+}
+
+/*!
+ * \brief Returns an empty LocaleDetail.
+ */
+const LocaleDetail &LocaleDetail::getEmpty()
+{
+    static const auto empty = LocaleDetail();
+    return empty;
+}
+
+/*!
+ * \brief Returns the abbreviated name of the specified \a format.
+ *
+ * This function returns the \a format if present. Otherwise it returns an empty string. This might be
+ * improved in the future, e.g. to convert to the specified \a format. It would also be possible to combine
+ * multiple details. For instance, if BCP-47 is required but only an ISO language and a domain name country
+ * are present, both could be combined and returned as BCP-47 abbreviation.
+ */
+const LocaleDetail &Locale::abbreviatedName(LocaleFormat format) const
+{
+    for (const auto &detail : *this) {
+        if (!detail.empty() && detail.format == format && isLanguageDefined(detail)) {
+            return detail;
+        }
+    }
+    return LocaleDetail::getEmpty();
+}
+
+/*!
+ * \brief Returns *some* abbreviated name, *preferrably* of the specified \a preferredFormat.
+ *
+ * This function returns the \a preferredFormat if present. Otherwise it returns the most relevant
+ * detail. This might be improved in the future, e.g. to convert to the \a preferredFormat. It would
+ * also be possible to combine multiple details. For instance, if BCP-47 is preferred but only an ISO
+ * language and a domain name country are present, both could be combined and returned as BCP-47 abbreviation.
+ *
+ * Returns an empty string if no details are present.
+ *
+ * \remarks This function is intended to be used for display purposes when the exact format doesn't matter and
+ *          you just want to show the "best" abbreviation specified within the file.
+ */
+const LocaleDetail &Locale::someAbbreviatedName(LocaleFormat preferredFormat) const
+{
+    auto format = LocaleFormat::Unknown;
+    const LocaleDetail *mostRelevantDetail = nullptr;
+    for (const auto &detail : *this) {
+        if (!detail.empty()
+            && static_cast<std::underlying_type_t<LocaleFormat>>(detail.format) >= static_cast<std::underlying_type_t<LocaleFormat>>(format)) {
+            if (detail.format == preferredFormat) {
+                return detail;
+            }
+            format = detail.format;
+            mostRelevantDetail = &detail;
+        }
+    }
+    if (!mostRelevantDetail || !isLanguageDefined(*mostRelevantDetail)) {
+        return LocaleDetail::getEmpty();
+    }
+    return *mostRelevantDetail;
+}
+
+/*!
+ * \brief Returns the full name of the locale, e.g. Germany for the ISO code "ger" or an empty string if the
+ *        full name is not known.
+ * \remarks So far the full name is only known for ISO-639-2/B codes.
+ */
+const std::string &TagParser::Locale::fullName() const
+{
+    for (const auto &detail : *this) {
+        if (detail.format == LocaleFormat::ISO_639_2_B || detail.format == LocaleFormat::ISO_639_2_T) {
+            return languageNameFromIso(detail);
+        }
+    }
+    return LocaleDetail::getEmpty();
+}
+
+/*!
+ * \brief Returns the full name if possible and otherwise falls back to the abbreviated name.
+ * \remarks This function is intended to be used for display purposes.
+ */
+const std::string &Locale::fullOrSomeAbbreviatedName() const
+{
+    if (const auto &name = fullName(); !name.empty()) {
+        return name;
+    }
+    return someAbbreviatedName();
+}
+
+/*!
+ * \brief Returns all details as comma-separated string.
+ */
+std::string Locale::toString() const
+{
+    return CppUtilities::joinStrings<std::vector<LocaleDetail>, std::string>(*this, LocaleDetail(", "sv, LocaleFormat::Unknown), true);
+}
+
+} // namespace TagParser
diff --git a/localehelper.h b/localehelper.h
new file mode 100644
index 0000000..9acb1c0
--- /dev/null
+++ b/localehelper.h
@@ -0,0 +1,128 @@
+#ifndef TAG_PARSER_LANGUAGE_H
+#define TAG_PARSER_LANGUAGE_H
+
+#include "./global.h"
+
+#include <cstdint>
+#include <optional>
+#include <string>
+#include <utility>
+#include <vector>
+
+namespace TagParser {
+
+/*!
+ * \brief Returns whether an ISO-639-2 \a languageSpecification is not empty or undefined.
+ */
+inline bool isLanguageDefined(const std::string &languageSpecification)
+{
+    return !languageSpecification.empty() && languageSpecification != "und" && languageSpecification != "XXX";
+}
+
+TAG_PARSER_EXPORT const std::string &languageNameFromIso(const std::string &isoCode);
+TAG_PARSER_EXPORT const std::string &languageNameFromIsoWithFallback(const std::string &isoCode);
+
+/// \brief The LocaleFormat enum class specifies the format used by a LocaleDetail.
+enum class LocaleFormat : std::uint64_t {
+    Unknown, /**< the format is unknown */
+    DomainCountry, /**< a country as used by [Internet domains](https://www.iana.org/domains/root/db) (e.g. "de" for Germany or "at" for Austria) */
+    ISO_639_1, /**< a language specified via ISO-639-1 code (e.g. "de" for German) */
+    ISO_639_2_T, /**< a language specified via ISO-639-2/T code (terminological, e.g. "deu" for German) */
+    ISO_639_2_B, /**< a language specified via ISO-639-2/B code (bibliographic, e.g. "ger" for German) */
+    BCP_47, /**< a language and/or country according to [BCP 47](https://tools.ietf.org/html/bcp47) using
+                the [IANA Language Subtag Registry](https://www.iana.com/assignments/language-subtag-registry/language-subtag-registry)
+                (e.g. "de_DE" for the language/country German/Germany or "de_AT" for German/Austria) */
+};
+
+/// \brief The LocaleDetail struct specifies a language and/or country.
+struct TAG_PARSER_EXPORT LocaleDetail : public std::string {
+    explicit LocaleDetail();
+    explicit LocaleDetail(std::string_view value, LocaleFormat format);
+    explicit LocaleDetail(std::string &&value, LocaleFormat format);
+    LocaleFormat format = LocaleFormat::Unknown;
+    static const LocaleDetail &getEmpty();
+};
+
+/*!
+ * \brief Constructs an empty LocaleDetail.
+ */
+inline LocaleDetail::LocaleDetail()
+    : format(LocaleFormat::Unknown)
+{
+}
+
+/*!
+ * \brief Constructs a new LocaleDetail making a copy of \a value.
+ */
+inline LocaleDetail::LocaleDetail(std::string_view value, LocaleFormat format)
+    : std::string(value)
+    , format(format)
+{
+}
+
+/*!
+ * \brief Constructs a new LocaleDetail moving the specified \a value.
+ */
+inline LocaleDetail::LocaleDetail(std::string &&value, LocaleFormat format)
+    : std::string(std::move(value))
+    , format(format)
+{
+}
+
+/// \brief The Locale struct specifies a language and/or a country using one or more LocaleDetail objects.
+struct TAG_PARSER_EXPORT Locale : public std::vector<LocaleDetail> {
+    explicit Locale() = default;
+    explicit Locale(std::initializer_list<LocaleDetail> details);
+    explicit Locale(std::string &&value, LocaleFormat format);
+    explicit Locale(std::string_view value, LocaleFormat format);
+    const LocaleDetail &abbreviatedName(LocaleFormat format) const;
+    template <typename LocaleFormat, typename... LocaleFormats>
+    const LocaleDetail &abbreviatedName(LocaleFormat format, LocaleFormats... moreFormats) const;
+    const LocaleDetail &someAbbreviatedName(LocaleFormat preferredFormat = LocaleFormat::BCP_47) const;
+    const std::string &fullName() const;
+    const std::string &fullOrSomeAbbreviatedName() const;
+    std::string toString() const;
+};
+
+/*!
+ * \brief Returns the abbreviated name of the specified \a format; if not present, checks \a moreFormats.
+ */
+template <typename LocaleFormat, typename... LocaleFormats>
+inline const LocaleDetail &Locale::abbreviatedName(LocaleFormat format, LocaleFormats... moreFormats) const
+{
+    if (const auto &detail = abbreviatedName(format); !detail.empty()) {
+        return detail;
+    } else {
+        return abbreviatedName(moreFormats...);
+    }
+}
+
+/*!
+ * \brief Constructs a new locale with the specified \a details.
+ */
+inline Locale::Locale(std::initializer_list<LocaleDetail> details)
+    : std::vector<LocaleDetail>(details)
+{
+}
+
+/*!
+ * \brief Constructs a new locale with the specified \a value and \a format.
+ */
+inline Locale::Locale(std::string &&value, LocaleFormat format)
+    : std::vector<LocaleDetail>()
+{
+    emplace_back(std::move(value), format);
+}
+
+/*!
+ * \brief Constructs a new locale with the specified \a value and \a format.
+ */
+inline Locale::Locale(std::string_view value, LocaleFormat format)
+    : std::vector<LocaleDetail>()
+{
+    emplace_back(value, format);
+}
+
+} // namespace TagParser
+
+#endif // TAG_PARSER_LANGUAGE_H
diff --git a/matroska/matroskachapter.cpp b/matroska/matroskachapter.cpp
index 8e8145c..e1a23a7 100644
--- a/matroska/matroskachapter.cpp
+++ b/matroska/matroskachapter.cpp
@@ -99,15 +99,13 @@ void MatroskaChapter::internalParse(Diagnostics &diag)
                     }
                     break;
                 case MatroskaIds::ChapLanguage:
-                    m_names.back().languages().emplace_back(chapterDisplayElement->readString());
+                    m_names.back().locale().emplace_back(chapterDisplayElement->readString(), LocaleFormat::ISO_639_2_B);
                     break;
                 case MatroskaIds::ChapLanguageIETF:
-                    diag.emplace_back(DiagLevel::Warning,
-                        "\"ChapterDisplay\"-element contains a \"ChapLanguageIETF\"-element which is not supported yet. It will be ignored.",
-                        context);
+                    m_names.back().locale().emplace_back(chapterDisplayElement->readString(), LocaleFormat::BCP_47);
                     break;
                 case MatroskaIds::ChapCountry:
-                    m_names.back().countries().emplace_back(chapterDisplayElement->readString());
+                    m_names.back().locale().emplace_back(chapterDisplayElement->readString(), LocaleFormat::DomainCountry);
                     break;
                 }
             }
@@ -124,8 +122,8 @@ void MatroskaChapter::internalParse(Diagnostics &diag)
     }
     // "eng" is default language
     for (LocaleAwareString &name : m_names) {
-        if (name.languages().empty()) {
-            name.languages().emplace_back("eng");
+        if (name.locale().empty()) {
+            name.locale().emplace_back("eng"sv, LocaleFormat::ISO_639_2_B);
         }
     }
 }
diff --git a/matroska/matroskatagfield.cpp b/matroska/matroskatagfield.cpp
index ef8f90b..a78f2f2 100644
--- a/matroska/matroskatagfield.cpp
+++ b/matroska/matroskatagfield.cpp
@@ -87,13 +87,13 @@ void MatroskaTagField::reparse(EbmlElement &simpleTagElement, Diagnostics &diag,
             }
             break;
         case MatroskaIds::TagLanguage:
-            if (!tagLanguageFound && !tagLanguageIETFFound) {
+            if (!tagLanguageFound) {
                 tagLanguageFound = true;
-                string lng = child->readString();
-                if (lng != "und") {
-                    value().setLanguage(lng);
+                auto language = child->readString();
+                if (language != "und") {
+                    value().locale().emplace_back(std::move(language), LocaleFormat::ISO_639_2_B);
                 }
-            } else if (tagLanguageFound) {
+            } else {
                 diag.emplace_back(DiagLevel::Warning,
                     "\"SimpleTag\"-element contains multiple \"TagLanguage\"-elements. Surplus \"TagLanguage\"-elements will be ignored.", context);
             }
@@ -101,10 +101,7 @@ void MatroskaTagField::reparse(EbmlElement &simpleTagElement, Diagnostics &diag,
         case MatroskaIds::TagLanguageIETF:
             if (!tagLanguageIETFFound) {
                 tagLanguageIETFFound = true;
-                diag.emplace_back(DiagLevel::Warning,
-                    "\"SimpleTag\"-element contains a \"TagLanguageIETF\"-element. That's not supported at this point. The element will be dropped "
-                    "when applying changes.",
-                    context);
+                value().locale().emplace_back(child->readString(), LocaleFormat::BCP_47);
             } else {
                 diag.emplace_back(DiagLevel::Warning,
                     "\"SimpleTag\"-element contains multiple \"TagLanguageIETF\"-elements. Surplus \"TagLanguageIETF\"-elements will be ignored.",
@@ -192,6 +189,8 @@ void MatroskaTagField::make(ostream &stream, Diagnostics &diag)
  */
 MatroskaTagFieldMaker::MatroskaTagFieldMaker(MatroskaTagField &field, Diagnostics &diag)
     : m_field(field)
+    , m_language(m_field.value().locale().abbreviatedName(LocaleFormat::ISO_639_2_B, LocaleFormat::Unknown))
+    , m_languageIETF(m_field.value().locale().abbreviatedName(LocaleFormat::BCP_47))
     , m_isBinary(false)
 {
     try {
@@ -203,23 +202,29 @@ MatroskaTagFieldMaker::MatroskaTagFieldMaker(MatroskaTagField &field, Diagnostic
             "making Matroska \"SimpleTag\" element.");
         m_isBinary = true;
     }
-    size_t languageSize = m_field.value().language().size();
-    if (!languageSize) {
-        languageSize = 3; // if there's no language set, the 3 byte long value "und" is used
-    }
+
+    // compute size of the mandatory "TagLanguage" element (if there's no language set, the 3 byte long value "und" is used)
+    const auto languageSize = m_language.empty() ? 3 : m_language.size();
+    const auto languageElementSize = 2 + EbmlElement::calculateSizeDenotationLength(languageSize) + languageSize;
+    // compute size of the optional "TagLanguageIETF" element
+    const auto languageIETFElementSize
+        = m_languageIETF.empty() ? 0 : (2 + EbmlElement::calculateSizeDenotationLength(m_languageIETF.size()) + m_languageIETF.size());
+
+    // compute "SimpleTag" element size
     m_simpleTagSize =
         // "TagName" element
         +2 + EbmlElement::calculateSizeDenotationLength(m_field.id().size())
         + m_field.id().size()
-        // "TagLanguage" element
-        + 2 + EbmlElement::calculateSizeDenotationLength(languageSize)
-        + languageSize
+        // language elements
+        + languageElementSize
+        + languageIETFElementSize
         // "TagDefault" element
         + 2 + 1
         + 1
         // "TagString" element
         + 2 + EbmlElement::calculateSizeDenotationLength(m_stringValue.size()) + m_stringValue.size();
-    // nested tags
+
+    // compute size of nested tags
     for (auto &nestedField : field.nestedFields()) {
         m_nestedMaker.emplace_back(nestedField.prepareMaking(diag));
         m_simpleTagSize += m_nestedMaker.back().m_totalSize;
@@ -238,30 +243,37 @@ void MatroskaTagFieldMaker::make(ostream &stream) const
 {
     BinaryWriter writer(&stream);
     char buff[8];
-    // write header of "SimpleTag" element
+    // write "SimpleTag" element
     writer.writeUInt16BE(MatroskaIds::SimpleTag);
     std::uint8_t sizeDenotationLen = EbmlElement::makeSizeDenotation(m_simpleTagSize, buff);
     stream.write(buff, sizeDenotationLen);
-    // write header of "TagName" element
+    // write "TagName" element
     writer.writeUInt16BE(MatroskaIds::TagName);
     sizeDenotationLen = EbmlElement::makeSizeDenotation(m_field.id().size(), buff);
     stream.write(buff, sizeDenotationLen);
     stream.write(m_field.id().c_str(), m_field.id().size());
-    // write header of "TagLanguage" element
+    // write "TagLanguage" element
     writer.writeUInt16BE(MatroskaIds::TagLanguage);
-    if (m_field.value().language().empty()) {
+    if (m_language.empty()) {
         stream.put(static_cast<ostream::char_type>(0x80 | 3));
         stream.write("und", 3);
     } else {
-        sizeDenotationLen = EbmlElement::makeSizeDenotation(m_field.value().language().size(), buff);
+        sizeDenotationLen = EbmlElement::makeSizeDenotation(m_language.size(), buff);
         stream.write(buff, sizeDenotationLen);
-        stream.write(m_field.value().language().c_str(), m_field.value().language().size());
+        stream.write(m_language.data(), m_language.size());
     }
-    // write header of "TagDefault" element
+    // write "TagLanguageIETF" element
+    if (!m_languageIETF.empty()) {
+        writer.writeUInt16BE(MatroskaIds::TagLanguageIETF);
+        sizeDenotationLen = EbmlElement::makeSizeDenotation(m_languageIETF.size(), buff);
+        stream.write(buff, sizeDenotationLen);
+        stream.write(m_languageIETF.data(), m_languageIETF.size());
+    }
+    // write "TagDefault" element
     writer.writeUInt16BE(MatroskaIds::TagDefault);
     stream.put(static_cast<ostream::char_type>(0x80 | 1));
     stream.put(m_field.isDefault() ? 1 : 0);
-    // write header of "TagString"/"TagBinary" element
+    // write "TagString"/"TagBinary" element
     if (m_isBinary) {
         writer.writeUInt16BE(MatroskaIds::TagBinary);
         sizeDenotationLen = EbmlElement::makeSizeDenotation(m_field.value().dataSize(), buff);
diff --git a/matroska/matroskatagfield.h b/matroska/matroskatagfield.h
index 86d252b..80d31ab 100644
--- a/matroska/matroskatagfield.h
+++ b/matroska/matroskatagfield.h
@@ -39,11 +39,13 @@ private:
     MatroskaTagFieldMaker(MatroskaTagField &field, Diagnostics &diag);
 
     MatroskaTagField &m_field;
-    bool m_isBinary;
     std::string m_stringValue;
+    const std::string &m_language;
+    const std::string &m_languageIETF;
     std::uint64_t m_simpleTagSize;
     std::uint64_t m_totalSize;
     std::vector<MatroskaTagFieldMaker> m_nestedMaker;
+    bool m_isBinary;
 };
 
 /*!
diff --git a/matroska/matroskatrack.cpp b/matroska/matroskatrack.cpp
index 2d07104..e74edb7 100644
--- a/matroska/matroskatrack.cpp
+++ b/matroska/matroskatrack.cpp
@@ -409,11 +409,10 @@ void MatroskaTrack::internalParseHeader(Diagnostics &diag)
             m_name = trackInfoElement->readString();
             break;
         case MatroskaIds::TrackLanguage:
-            m_language = trackInfoElement->readString();
+            m_locale.emplace_back(trackInfoElement->readString(), LocaleFormat::ISO_639_2_B);
             break;
         case MatroskaIds::TrackLanguageIETF:
-            diag.emplace_back(DiagLevel::Warning,
-                "\"TrackEntry\"-element contains a \"LanguageIETF\"-element which is not supported yet. It will be ignored.", context);
+            m_locale.emplace_back(trackInfoElement->readString(), LocaleFormat::BCP_47);
             break;
         case MatroskaIds::CodecID:
             m_format = codecIdToMediaFormat(m_formatId = trackInfoElement->readString());
@@ -539,8 +538,8 @@ void MatroskaTrack::internalParseHeader(Diagnostics &diag)
     }
 
     // set English if no language has been specified (it is default value of MatroskaIds::TrackLanguage)
-    if (m_language.empty()) {
-        m_language = "eng";
+    if (m_locale.empty()) {
+        m_locale.emplace_back("eng"sv, LocaleFormat::ISO_639_2_B);
     }
 }
 
@@ -557,6 +556,8 @@ void MatroskaTrack::internalParseHeader(Diagnostics &diag)
  */
 MatroskaTrackHeaderMaker::MatroskaTrackHeaderMaker(const MatroskaTrack &track, Diagnostics &diag)
     : m_track(track)
+    , m_language(m_track.locale().abbreviatedName(LocaleFormat::ISO_639_2_B, LocaleFormat::Unknown))
+    , m_languageIETF(m_track.locale().abbreviatedName(LocaleFormat::BCP_47))
     , m_dataSize(0)
 {
     CPP_UTILITIES_UNUSED(diag);
@@ -570,9 +571,14 @@ MatroskaTrackHeaderMaker::MatroskaTrackHeaderMaker(const MatroskaTrack &track, D
     if (!m_track.name().empty()) {
         m_dataSize += 2 + EbmlElement::calculateSizeDenotationLength(m_track.name().size()) + m_track.name().size();
     }
-    if (!m_track.language().empty()) {
-        m_dataSize += 3 + EbmlElement::calculateSizeDenotationLength(m_track.language().size()) + m_track.language().size();
-    }
+
+    // compute size of the mandatory "Language" element (if there's no language set, the 3 byte long value "und" is used)
+    const auto languageSize = m_language.empty() ? 3 : m_language.size();
+    const auto languageElementSize = 3 + EbmlElement::calculateSizeDenotationLength(languageSize) + languageSize;
+    // compute size of the optional "LanguageIETF" element
+    const auto languageIETFElementSize
+        = m_languageIETF.empty() ? 0 : (3 + EbmlElement::calculateSizeDenotationLength(m_languageIETF.size()) + m_languageIETF.size());
+    m_dataSize += languageElementSize + languageIETFElementSize;
 
     // calculate size for other elements
     for (EbmlElement *trackInfoElement = m_track.m_trackElement->firstChild(); trackInfoElement; trackInfoElement = trackInfoElement->nextSibling()) {
@@ -581,6 +587,7 @@ MatroskaTrackHeaderMaker::MatroskaTrackHeaderMaker(const MatroskaTrack &track, D
         case MatroskaIds::TrackUID:
         case MatroskaIds::TrackName:
         case MatroskaIds::TrackLanguage:
+        case MatroskaIds::TrackLanguageIETF:
         case MatroskaIds::TrackFlagEnabled:
         case MatroskaIds::TrackFlagDefault:
         case MatroskaIds::TrackFlagForced:
@@ -619,8 +626,9 @@ void MatroskaTrackHeaderMaker::make(ostream &stream) const
     if (!m_track.name().empty()) {
         EbmlElement::makeSimpleElement(stream, MatroskaIds::TrackName, m_track.name());
     }
-    if (!m_track.language().empty()) {
-        EbmlElement::makeSimpleElement(stream, MatroskaIds::TrackLanguage, m_track.language());
+    EbmlElement::makeSimpleElement(stream, MatroskaIds::TrackLanguage, m_language.empty() ? "und" : m_language);
+    if (!m_languageIETF.empty()) {
+        EbmlElement::makeSimpleElement(stream, MatroskaIds::TrackLanguageIETF, m_languageIETF);
     }
 
     // make other elements
diff --git a/matroska/matroskatrack.h b/matroska/matroskatrack.h
index 861cc62..afd1204 100644
--- a/matroska/matroskatrack.h
+++ b/matroska/matroskatrack.h
@@ -22,6 +22,8 @@ private:
     MatroskaTrackHeaderMaker(const MatroskaTrack &track, Diagnostics &diag);
 
     const MatroskaTrack &m_track;
+    const std::string &m_language;
+    const std::string &m_languageIETF;
     std::uint64_t m_dataSize;
     std::uint64_t m_requiredSize;
     std::uint8_t m_sizeDenotationLength;
diff --git a/mediafileinfo.cpp b/mediafileinfo.cpp
index fd6269c..2630291 100644
--- a/mediafileinfo.cpp
+++ b/mediafileinfo.cpp
@@ -3,7 +3,7 @@
 #include "./backuphelper.h"
 #include "./diagnostics.h"
 #include "./exceptions.h"
-#include "./language.h"
+#include "./locale.h"
 #include "./progressfeedback.h"
 #include "./signature.h"
 #include "./tag.h"
@@ -914,13 +914,18 @@ unordered_set<string> MediaFileInfo::availableLanguages(MediaType type) const
     unordered_set<string> res;
     if (m_container) {
         for (size_t i = 0, count = m_container->trackCount(); i != count; ++i) {
-            const AbstractTrack *track = m_container->track(i);
-            if ((type == MediaType::Unknown || track->mediaType() == type) && isLanguageDefined(track->language())) {
-                res.emplace(track->language());
+            const AbstractTrack *const track = m_container->track(i);
+            if (type != MediaType::Unknown && track->mediaType() != type) {
+                continue;
+            }
+            if (const auto &language = track->locale().someAbbreviatedName(); !language.empty()) {
+                res.emplace(language);
             }
         }
-    } else if (m_singleTrack && (type == MediaType::Unknown || m_singleTrack->mediaType() == type) && isLanguageDefined(m_singleTrack->language())) {
-        res.emplace(m_singleTrack->language());
+    } else if (m_singleTrack && (type == MediaType::Unknown || m_singleTrack->mediaType() == type)) {
+        if (const auto &language = m_singleTrack->locale().someAbbreviatedName(); !language.empty()) {
+            res.emplace(language);
+        }
     }
     return res;
 }
diff --git a/mp4/mp4tagfield.cpp b/mp4/mp4tagfield.cpp
index 218d061..834e985 100644
--- a/mp4/mp4tagfield.cpp
+++ b/mp4/mp4tagfield.cpp
@@ -541,7 +541,7 @@ Mp4TagFieldMaker::Mp4TagFieldMaker(Mp4TagField &field, Diagnostics &diag)
                 }
             }
         }
-    } catch (ConversionException &ex) {
+    } catch (const ConversionException &ex) {
         // it was not possible to perform required conversions
         if (char_traits<char>::length(ex.what())) {
             diag.emplace_back(DiagLevel::Critical, ex.what(), context);
diff --git a/mp4/mp4track.cpp b/mp4/mp4track.cpp
index 826b323..f7ea73d 100644
--- a/mp4/mp4track.cpp
+++ b/mp4/mp4track.cpp
@@ -1293,30 +1293,31 @@ void Mp4Track::makeMedia(Diagnostics &diag)
         writer().writeUInt32BE(static_cast<std::uint32_t>(duration));
     }
     // convert and write language
-    std::uint16_t language = 0;
+    const std::string &language = m_locale.abbreviatedName(LocaleFormat::ISO_639_2_T, LocaleFormat::Unknown);
+    std::uint16_t codedLanguage = 0;
     for (size_t charIndex = 0; charIndex != 3; ++charIndex) {
-        const char langChar = charIndex < m_language.size() ? m_language[charIndex] : 0;
+        const char langChar = charIndex < language.size() ? language[charIndex] : 0;
         if (langChar >= 'a' && langChar <= 'z') {
-            language |= static_cast<std::uint16_t>(langChar - 0x60) << (0xA - charIndex * 0x5);
+            codedLanguage |= static_cast<std::uint16_t>(langChar - 0x60) << (0xA - charIndex * 0x5);
             continue;
         }
 
         // handle invalid characters
-        if (m_language.empty()) {
+        if (language.empty()) {
             // preserve empty language field
-            language = 0;
+            codedLanguage = 0;
             break;
         }
-        diag.emplace_back(DiagLevel::Warning, "Assigned language \"" % m_language + "\" is of an invalid format. Setting language to undefined.",
-            "making mdhd atom");
-        language = 0x55C4; // und(efined)
+        diag.emplace_back(
+            DiagLevel::Warning, "Assigned language \"" % language + "\" is of an invalid format. Setting language to undefined.", "making mdhd atom");
+        codedLanguage = 0x55C4; // und(efined)
         break;
     }
-    if (m_language.size() > 3) {
+    if (language.size() > 3) {
         diag.emplace_back(
-            DiagLevel::Warning, "Assigned language \"" % m_language + "\" is longer than 3 byte and hence will be truncated.", "making mdhd atom");
+            DiagLevel::Warning, "Assigned language \"" % language + "\" is longer than 3 byte and hence will be truncated.", "making mdhd atom");
     }
-    writer().writeUInt16BE(language);
+    writer().writeUInt16BE(codedLanguage);
     writer().writeUInt16BE(0); // pre defined
     // write hdlr atom
     writer().writeUInt32BE(33 + m_name.size()); // size
@@ -1588,9 +1589,9 @@ void Mp4Track::internalParseHeader(Diagnostics &diag)
             static_cast<char>(((tmp & 0x03E0) >> 0x5) + 0x60),
             static_cast<char>(((tmp & 0x001F) >> 0x0) + 0x60),
         };
-        m_language = string(buff, 3);
+        m_locale.emplace_back(std::string(buff, 3), LocaleFormat::ISO_639_2_T);
     } else {
-        m_language.clear();
+        m_locale.clear();
     }
 
     // read hdlr atom
diff --git a/tagvalue.cpp b/tagvalue.cpp
index 837f7de..6e34c6d 100644
--- a/tagvalue.cpp
+++ b/tagvalue.cpp
@@ -97,7 +97,7 @@ TagValue::TagValue(const TagValue &other)
     : m_size(other.m_size)
     , m_desc(other.m_desc)
     , m_mimeType(other.m_mimeType)
-    , m_language(other.m_language)
+    , m_locale(other.m_locale)
     , m_type(other.m_type)
     , m_encoding(other.m_encoding)
     , m_descEncoding(other.m_descEncoding)
@@ -121,7 +121,7 @@ TagValue &TagValue::operator=(const TagValue &other)
     m_type = other.m_type;
     m_desc = other.m_desc;
     m_mimeType = other.m_mimeType;
-    m_language = other.m_language;
+    m_locale = other.m_locale;
     m_flags = other.m_flags;
     m_encoding = other.m_encoding;
     m_descEncoding = other.m_descEncoding;
@@ -183,7 +183,7 @@ bool TagValue::compareTo(const TagValue &other, TagValueComparisionFlags options
     // check whether meta-data is equal (except description)
     if (!(options & TagValueComparisionFlags::IgnoreMetaData)) {
         // check meta-data which always uses UTF-8 (everything but description)
-        if (m_mimeType != other.m_mimeType || m_language != other.m_language || m_flags != other.m_flags) {
+        if (m_mimeType != other.m_mimeType || m_locale != other.m_locale || m_flags != other.m_flags) {
             return false;
         }
 
@@ -307,7 +307,7 @@ void TagValue::clearMetadata()
 {
     m_desc.clear();
     m_mimeType.clear();
-    m_language.clear();
+    m_locale.clear();
     m_flags = TagValueFlags::None;
     m_encoding = TagTextEncoding::Latin1;
     m_descEncoding = TagTextEncoding::Latin1;
diff --git a/tagvalue.h b/tagvalue.h
index b633685..38b5cf9 100644
--- a/tagvalue.h
+++ b/tagvalue.h
@@ -1,6 +1,7 @@
 #ifndef TAG_PARSER_TAGVALUE_H
 #define TAG_PARSER_TAGVALUE_H
 
+#include "./localehelper.h"
 #include "./positioninset.h"
 
 #include <c++utilities/chrono/datetime.h>
@@ -143,8 +144,9 @@ public:
     void setDescription(const std::string &value, TagTextEncoding encoding = TagTextEncoding::Latin1);
     const std::string &mimeType() const;
     void setMimeType(const std::string &mimeType);
-    const std::string &language() const;
-    void setLanguage(const std::string &language);
+    const Locale &locale() const;
+    Locale &locale();
+    void setLocale(const Locale &locale);
     TagValueFlags flags() const;
     void setFlags(TagValueFlags flags);
     bool isLabeledAsReadonly() const;
@@ -188,7 +190,7 @@ private:
     std::size_t m_size;
     std::string m_desc;
     std::string m_mimeType;
-    std::string m_language;
+    Locale m_locale;
     std::unordered_map<std::string, std::string> m_nativeData;
     TagDataType m_type;
     TagTextEncoding m_encoding;
@@ -597,31 +599,45 @@ inline void TagValue::setMimeType(const std::string &mimeType)
 }
 
 /*!
- * \brief Returns the language.
+ * \brief Returns the locale.
  * \remarks
  * - Whether this additional meta-data is available and can be used depends on the tag format. It will
  *   be ignored by the implementation of the tag format if not supported.
- * - The format of the language is specific to the tag format. The implementation of the tag format might
+ * - The format of the locale is specific to the tag format. The implementation of the tag format might
  *   store the value without further validation.
- * \sa setLanguage()
+ * \sa setLocale()
  */
-inline const std::string &TagValue::language() const
+inline const Locale &TagValue::locale() const
 {
-    return m_language;
+    return m_locale;
 }
 
 /*!
- * \brief Sets the language.
+ * \brief Returns the locale.
  * \remarks
  * - Whether this additional meta-data is available and can be used depends on the tag format. It will
  *   be ignored by the implementation of the tag format if not supported.
- * - The format of the language is specific to the tag format. The implementation of the tag format might
+ * - The format of the locale is specific to the tag format. The implementation of the tag format might
  *   store the value without further validation.
- * \sa language()
+ * \sa setLocale()
  */
-inline void TagValue::setLanguage(const std::string &language)
+inline Locale &TagValue::locale()
 {
-    m_language = language;
+    return m_locale;
+}
+
+/*!
+ * \brief Sets the setLocale.
+ * \remarks
+ * - Whether this additional meta-data is available and can be used depends on the tag format. It will
+ *   be ignored by the implementation of the tag format if not supported.
+ * - The format of the locale is specific to the tag format. The implementation of the tag format might
+ *   store the value without further validation.
+ * \sa locale()
+ */
+inline void TagValue::setLocale(const Locale &locale)
+{
+    m_locale = locale;
 }
 
 /*!
diff --git a/tests/helper.h b/tests/helper.h
index 2d9539c..a7ac05d 100644
--- a/tests/helper.h
+++ b/tests/helper.h
@@ -2,6 +2,7 @@
 #define TAGPARSER_TEST_HELPER
 
 #include "../diagnostics.h"
+#include "../localehelper.h"
 #include "../size.h"
 #include "../tagvalue.h"
 
@@ -47,6 +48,14 @@ inline std::ostream &operator<<(std::ostream &os, const TagParser::DiagMessage &
     return os << diagMessage.levelName() << ':' << ' ' << diagMessage.message() << ' ' << '(' << diagMessage.context() << ')';
 }
 
+/*!
+ * \brief Prints a Locale to enable using it in CPPUNIT_ASSERT_EQUAL.
+ */
+inline std::ostream &operator<<(std::ostream &os, const TagParser::Locale &locale)
+{
+    return os << locale.toString();
+}
+
 } // namespace CppUtilities
 
 #endif // TAGPARSER_TEST_HELPER
diff --git a/tests/mediafileinfo.cpp b/tests/mediafileinfo.cpp
index 06bfd91..8c57208 100644
--- a/tests/mediafileinfo.cpp
+++ b/tests/mediafileinfo.cpp
@@ -182,7 +182,7 @@ void MediaFileInfoTests::testFullParseAndFurtherProperties()
     CPPUNIT_ASSERT_EQUAL(DiagLevel::Critical, diag.level());
 
     // track info / available languages
-    file.tracks().back()->setLanguage("eng");
+    file.tracks().back()->setLocale(Locale("eng"sv, LocaleFormat::ISO_639_2_B));
     CPPUNIT_ASSERT_EQUAL(unordered_set<string>({ "eng" }), file.availableLanguages());
     CPPUNIT_ASSERT_EQUAL(unordered_set<string>({}), file.availableLanguages(MediaType::Text));
     CPPUNIT_ASSERT_EQUAL("ID: 2422994868, type: Video"s, file.tracks()[0]->label());
diff --git a/tests/overallmkv.cpp b/tests/overallmkv.cpp
index f5c21c6..ce4e970 100644
--- a/tests/overallmkv.cpp
+++ b/tests/overallmkv.cpp
@@ -186,14 +186,14 @@ void OverallTests::checkMkvTestfile4()
             switch (m_tagStatus) {
             case TagStatus::Original:
             case TagStatus::Removed:
-                CPPUNIT_ASSERT_EQUAL("und"s, track->language());
+                CPPUNIT_ASSERT_EQUAL(Locale("und"sv, LocaleFormat::ISO_639_2_B), track->locale());
                 CPPUNIT_ASSERT_EQUAL(string(), track->name());
                 CPPUNIT_ASSERT(track->isEnabled());
                 CPPUNIT_ASSERT(!track->isForced());
                 CPPUNIT_ASSERT(!track->isDefault());
                 break;
             case TagStatus::TestMetaDataPresent:
-                CPPUNIT_ASSERT_EQUAL("ger"s, track->language());
+                CPPUNIT_ASSERT_EQUAL(Locale("ger"sv, LocaleFormat::ISO_639_2_B), track->locale());
                 CPPUNIT_ASSERT_EQUAL("the name"s, track->name());
                 CPPUNIT_ASSERT(track->isEnabled());
                 CPPUNIT_ASSERT(track->isForced());
@@ -245,7 +245,7 @@ void OverallTests::checkMkvTestfile5()
         case 3554194305:
             CPPUNIT_ASSERT_EQUAL(MediaType::Text, track->mediaType());
             CPPUNIT_ASSERT_EQUAL(GeneralMediaFormat::TextSubtitle, track->format().general);
-            CPPUNIT_ASSERT_EQUAL("ger"s, track->language());
+            CPPUNIT_ASSERT_EQUAL(Locale("ger"sv, LocaleFormat::ISO_639_2_B), track->locale());
             break;
         default:;
         }
@@ -599,7 +599,7 @@ void OverallTests::setMkvTestMetaData()
         // also change language, name, forced and default of track "3171450505" to German
         MatroskaTrack *track = container->trackById(3171450505);
         CPPUNIT_ASSERT(track);
-        track->setLanguage("ger");
+        track->setLocale(Locale("ger"sv, LocaleFormat::ISO_639_2_B));
         track->setName("the name");
         track->setDefault(true);
         track->setEnabled(true);
diff --git a/tests/overallmp4.cpp b/tests/overallmp4.cpp
index 1850aaf..c3f1333 100644
--- a/tests/overallmp4.cpp
+++ b/tests/overallmp4.cpp
@@ -84,7 +84,7 @@ void OverallTests::checkMp4Testfile2()
             CPPUNIT_ASSERT_EQUAL(static_cast<unsigned char>(SubFormats::AacMpeg4LowComplexityProfile), track->format().sub);
             CPPUNIT_ASSERT(!(track->format().extension & ExtensionFormats::SpectralBandReplication));
             CPPUNIT_ASSERT(!(track->format().extension & ExtensionFormats::ParametricStereo));
-            CPPUNIT_ASSERT_EQUAL("eng"s, track->language());
+            CPPUNIT_ASSERT_EQUAL(Locale("eng"sv, LocaleFormat::ISO_639_2_T), track->locale());
             CPPUNIT_ASSERT_EQUAL(2013, track->creationTime().year());
             CPPUNIT_ASSERT_EQUAL(48000u, track->samplingFrequency());
             CPPUNIT_ASSERT_EQUAL(static_cast<unsigned char>(Mpeg4ChannelConfigs::FrontLeftFrontRight), track->channelConfig());
@@ -92,13 +92,13 @@ void OverallTests::checkMp4Testfile2()
         case 3:
             CPPUNIT_ASSERT_EQUAL(MediaType::Audio, track->mediaType());
             CPPUNIT_ASSERT_EQUAL(GeneralMediaFormat::Ac3, track->format().general);
-            CPPUNIT_ASSERT_EQUAL("eng"s, track->language());
+            CPPUNIT_ASSERT_EQUAL(Locale("eng"sv, LocaleFormat::ISO_639_2_T), track->locale());
             CPPUNIT_ASSERT_EQUAL(2013, track->creationTime().year());
             break;
         case 4:
             CPPUNIT_ASSERT_EQUAL(MediaType::Audio, track->mediaType());
             CPPUNIT_ASSERT_EQUAL(GeneralMediaFormat::DtsHd, track->format().general);
-            CPPUNIT_ASSERT_EQUAL("eng"s, track->language());
+            CPPUNIT_ASSERT_EQUAL(Locale("eng"sv, LocaleFormat::ISO_639_2_T), track->locale());
             CPPUNIT_ASSERT_EQUAL(2013, track->creationTime().year());
             break;
         case 6:
@@ -296,7 +296,7 @@ void OverallTests::checkMp4Testfile6()
             CPPUNIT_ASSERT_EQUAL(static_cast<unsigned char>(SubFormats::AacMpeg4LowComplexityProfile), track->format().sub);
             CPPUNIT_ASSERT(!(track->format().extension & ExtensionFormats::SpectralBandReplication));
             CPPUNIT_ASSERT(!(track->format().extension & ExtensionFormats::ParametricStereo));
-            CPPUNIT_ASSERT_EQUAL("ger"s, track->language());
+            CPPUNIT_ASSERT_EQUAL(Locale("ger"sv, LocaleFormat::ISO_639_2_T), track->locale());
             CPPUNIT_ASSERT_EQUAL("test"s, track->name());
             CPPUNIT_ASSERT_EQUAL(2013, track->creationTime().year());
             CPPUNIT_ASSERT_EQUAL(48000u, track->samplingFrequency());
@@ -305,13 +305,13 @@ void OverallTests::checkMp4Testfile6()
         case 3:
             CPPUNIT_ASSERT_EQUAL(MediaType::Audio, track->mediaType());
             CPPUNIT_ASSERT_EQUAL(GeneralMediaFormat::Ac3, track->format().general);
-            CPPUNIT_ASSERT_EQUAL("eng"s, track->language());
+            CPPUNIT_ASSERT_EQUAL(Locale("eng"sv, LocaleFormat::ISO_639_2_T), track->locale());
             CPPUNIT_ASSERT_EQUAL(2013, track->creationTime().year());
             break;
         case 4:
             CPPUNIT_ASSERT_EQUAL(MediaType::Audio, track->mediaType());
             CPPUNIT_ASSERT_EQUAL(GeneralMediaFormat::DtsHd, track->format().general);
-            CPPUNIT_ASSERT_EQUAL("eng"s, track->language());
+            CPPUNIT_ASSERT_EQUAL(Locale("eng"sv, LocaleFormat::ISO_639_2_T), track->locale());
             CPPUNIT_ASSERT_EQUAL(2013, track->creationTime().year());
             break;
         case 5:
@@ -513,7 +513,7 @@ void OverallTests::alterMp4Tracks()
     container->addTrack(track);
     CPPUNIT_ASSERT_EQUAL(6_st, container->trackCount());
     auto &secondTrack = container->tracks()[1];
-    secondTrack->setLanguage("ger");
+    secondTrack->setLocale(Locale("ger"sv, LocaleFormat::ISO_639_2_T));
     secondTrack->setName("test");
 }