[BUG] Proper support for more than 2 letters language files

[moruzerinho6]

Please give System Info

Not required

Please give your StepMania Info

StepMania Version: 4.9.7GG
Theme: default

Describe the problem

Most language files use 2 letters naming such as en.ini, de.ini... and such files can have their naming defined inside of their own values, such as en.ini showing as English on the themes. However, if the language file has more than 2 letters, let's say pt-BR.ini, it's not possible to show its correct naming on the theme.

Describe what should happen

It should be possible to show the language correct name.

[moruzerinho6]

A good standard to follow when this is fixed is ISO 639-X

[Scraticus]

this is in engine, but needs some other work done first so will close, and then poke you when you can use them.