Introduce display language setting

[Kissaki]

It would be nice if DeaDBeeF would allow setting the display language.

I'm sure there's scenarios and use cases where a user may want to run it under a different display language then other programs or the OS.

It would mitigate / enable working around issues like #3049, or if a particular translation is not of high quality or confusing to the user (terminology etc).

A comment in #2495 mentions being able to change the display language through an environment variable (LANG). Interacting with environment variables is not obvious nor accessible to the average user. On Windows at least, creating a shortcut and adding a parameter is not sufficient to do so either, requiring additional layers for a convoluted workaround.