set language per show?

[TheDreadPirate]

thanks

too bad - follow up, though not jellyfin related...is there an easy way to change the default audio-track of an mkv's tracks?
or is there a plugin that could help selecting a preferred language?

You can use MKVToolNix or ffmpeg to change the default audio track.  In most clients, this should result in that track being selected when you initiate playback.