diff --git a/matroska/matroskaid.cpp b/matroska/matroskaid.cpp
index d439bff..a0cca63 100644
--- a/matroska/matroskaid.cpp
+++ b/matroska/matroskaid.cpp
@@ -140,6 +140,8 @@ const char *matroskaIdName(std::uint32_t matroskaId)
         return "track name";
     case TrackLanguage:
         return "track language";
+    case TrackLanguageIETF:
+        return "track language IETF";
     case TrackFlagEnabled:
         return "track enabled";
     case TrackFlagDefault:
@@ -290,6 +292,8 @@ const char *matroskaIdName(std::uint32_t matroskaId)
         return "tag string";
     case TagLanguage:
         return "tag language";
+    case TagLanguageIETF:
+        return "tag language IETF";
     case TagDefault:
         return "tag default";
     case TagBinary:
@@ -418,6 +422,8 @@ const char *matroskaIdName(std::uint32_t matroskaId)
         return "chap string";
     case ChapLanguage:
         return "chap language";
+    case ChapLanguageIETF:
+        return "chap language IETF";
     case ChapCountry:
         return "chap country";
 
@@ -596,6 +602,7 @@ MatroskaElementLevel matroskaIdLevel(std::uint32_t matroskaId)
     case MaxBlockAdditionId:
     case TrackName:
     case TrackLanguage:
+    case TrackLanguageIETF:
     case CodecID:
     case CodecPrivate:
     case CodecName:
diff --git a/matroska/matroskaid.h b/matroska/matroskaid.h
index f14f509..4f0806d 100644
--- a/matroska/matroskaid.h
+++ b/matroska/matroskaid.h
@@ -88,6 +88,7 @@ enum TrackEntryIds {
     MaxBlockAdditionId = 0x55EE,
     TrackName = 0x536E,
     TrackLanguage = 0x22B59C,
+    TrackLanguageIETF = 0x22B59D,
     CodecID = 0x86,
     CodecPrivate = 0x63A2,
     CodecName = 0x258688,
@@ -219,6 +220,7 @@ enum SimpleTagIds {
     TagName = 0x45A3,
     TagString = 0x4487,
     TagLanguage = 0x447A,
+    TagLanguageIETF = 0x447B,
     TagDefault = 0x4484,
     TagBinary = 0x4485,
 };
@@ -324,7 +326,7 @@ enum ChapterTrackIds { ChapterTrackNumber = 0x89 };
 /*!
  * \brief Encapsulates all ID values in the ChapterDisplay master.
  */
-enum ChapterDisplayIds { ChapString = 0x85, ChapLanguage = 0x437c, ChapCountry = 0x437e };
+enum ChapterDisplayIds { ChapString = 0x85, ChapLanguage = 0x437c, ChapLanguageIETF = 0x437D, ChapCountry = 0x437e };
 
 /*!
  * \brief Encapsulates all ID values in the ChapProcess master.