text: Title: Libdoc's default language selection does not support all available languages
  Body: The CLI help and input validation only allow FI, and EN as input for the `--language` switch, but more languages are currently available.
  
  Ideally this should be dynamic, but at least both the helptext for libdoc language switch and the validator should reflect what's available.
  
  https://github.com/robotframework/robotframework/blob/986351665e304db25b1a77e60384624e21ea943d/src/robot/libdoc.py#L234