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).
Parameters
lang_code: string
ISO-639 language code (e.g. "deu" or "ger" or "de")
Returns boolean
TRUE if the two- or three-letter language code in lang_code is a valid ISO-639 language code.
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).