Check if a given string contains a known ISO 639 language code.
This is useful in situations where it's not clear whether a given
string is a language code (which should be put into a #GST_TAG_LANGUAGE_CODE
tag) or a free-form language name descriptor (which should be put into a
#GST_TAG_LANGUAGE_NAME tag instead).
Check if a given string contains a known ISO 639 language code.
This is useful in situations where it's not clear whether a given string is a language code (which should be put into a #GST_TAG_LANGUAGE_CODE tag) or a free-form language name descriptor (which should be put into a #GST_TAG_LANGUAGE_NAME tag instead).