Improve language tag support

[strahlc]

The id3 standard[1] says that the TLAN tag should be a three letter representation according ISO-639-2 [2].

The language is represented with three characters according to ISO-639-2 [ISO-639-2]. If more than one language is used in the text their language codes should follow according to the amount of their usage, e.g. "eng" $00 "sve" $00

Maybe we can add a list of (translateable) language names[2]. This way the user see "Englisch", "French", "German", ... in the language column instead of "eng", "fra", "ger", ... .

Furthermore, in the track properties dialog, the user doesn't need to know the language code for the languages, he can just pick one from a drop down list.

[1] http://id3.org/id3v2.4.0-frames
[2] https://en.wikipedia.org/wiki/List_of_ISO_639-2_codes

[sbrubes]

Years ago I remember a request (that I couldn't found now) saying about adding support for ID3v2.4.

At that occasion, I've worked on a new Track Properties that has improvements for all tags, including what you are asking.

This code it's on an old machine here, but if you think it's a good idea I could find it.

[virtuald]

@sbrubes the current track properties dialog is not particularly polished, so I would welcome any improvements that you have