Multilanguage: Add utility to get language names consistently

There are multiple places that language codes are converted
to language names each doing it a different way. To make
this consistent, we need to have a single implementation
for it.

Change-Id: I2aeaf5b7c9203e8a41a61420f4c98e1fce491db5
Reviewed-by: <github-actions-qt-creator@cristianadam.eu>
Reviewed-by: hjk <hjk@qt.io>
Reviewed-by: Eike Ziller <eike.ziller@qt.io>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>

src/libs/utils/stringutils.cpp

@@ -34,6 +34,7 @@
 #include <QDir>
 #include <QJsonArray>
 #include <QJsonValue>
+#include <QLocale>
 #include <QRegularExpression>
 #include <QSet>
 #include <QTime>
@@ -464,4 +465,16 @@ QString wildcardToRegularExpression(const QString &original)
     return "\\A" + rx + "\\z";
 #endif
 }
+
+QTCREATOR_UTILS_EXPORT QString languageNameFromLanguageCode(const QString &languageCode)
+{
+    QLocale locale(languageCode);
+    QString languageName = QLocale::languageToString(locale.language());
+    QString nativeLanguageName = locale.nativeLanguageName().simplified();
+
+    if (!nativeLanguageName.isEmpty() && languageName != nativeLanguageName)
+        languageName += " - " + locale.nativeLanguageName();
+    return languageName;
+}
+
 } // namespace Utils

src/libs/utils/stringutils.h

@@ -121,4 +121,7 @@ QTCREATOR_UTILS_EXPORT QString formatElapsedTime(qint64 elapsed);
  * into account and handling them to disallow matching a wildcard characters.
  */
 QTCREATOR_UTILS_EXPORT QString wildcardToRegularExpression(const QString &original);
+
+QTCREATOR_UTILS_EXPORT QString languageNameFromLanguageCode(const QString &languageCode);
+
 } // namespace Utils