Have you subscribed to codecombat?
If no
Only the first 5 levels are free, and don’t provide much coding knowledge
It mostly only uses the hero.move[up,down,left,right]() commands, which are in CodeCombat’s library, or, to word it differently, not useful in real coding.
Since these levels give little coding insight, the CodeCombat team likely decided that there was no point being able to switch languages.
The free levels appear to serve more as an introduction to the game.
Summary - Only first 5 levels are free, can’t change language unless subscribed, subscription ~£10/month
If yes
Contact customer support at support@codecombat.com via email, explaining the situation and that you can’t access subscriber features even though you’re paying for premium.
Hopefully this helps to resolve the issue, if not, ping me @MarmiteOnToast and I’ll do my best to assist further