Allow tracking whether the locale has changed via the `QtSettings` class

This allows an application to reload translations if the default locale has
changed to apply locale changes dynamically.

settingsdialog/qtsettings.cpp

@@ -50,6 +50,7 @@ struct QtSettingsData {
     QString iconTheme;
     QString initialIconTheme;
     QLocale defaultLocale;
+    QLocale previousLocale;
     QString localeName;
     QString previousPluginDirectory;
     QString additionalPluginDirectory;
@@ -319,6 +320,7 @@ void QtSettings::apply()
     }
 
     // apply locale
+    m_d->previousLocale = QLocale();
     QLocale::setDefault(m_d->customLocale ? QLocale(m_d->localeName) : m_d->defaultLocale);
 }
 
@@ -355,6 +357,14 @@ bool QtSettings::isPaletteDark()
     return m_d->isPaletteDark;
 }
 
+/*!
+ * \brief Returns whether the last apply() call has changed the default locale.
+ */
+bool QtSettings::hasLocaleChanged() const
+{
+    return m_d->previousLocale != QLocale();
+}
+
 /*!
  * \brief Returns a new OptionCatecory containing all Qt related option pages.
  * \remarks

settingsdialog/qtsettings.h

@@ -53,6 +53,7 @@ public:
     void reevaluatePaletteAndDefaultIconTheme();
     bool isPaletteDark();
     bool hasCustomFont() const;
+    bool hasLocaleChanged() const;
     operator QtSettingsData &() const;
 
     OptionCategory *category();