So I found that the names of the new biomes are not translated (they have raw translation strings).
MC-237167
New Biome Names Are Untranslated
Resolved
Duplicate
1
(Unassigned)
Unconfirmed
(Unassigned)
language, language-file, missing-text
21w37a
Retrieved
Thank you for your report!
We're tracking this issue in MC-236609, so this ticket is being resolved and linked as a duplicate.
If you would like to add a vote and any extra information to the main ticket it would be appreciated.
If you haven't already, you might like to make use of the search feature to see if the issue has already been mentioned.
Quick Links:
📓 Bug Tracker Guidelines – 💬 Community Support – 📧 Mojang Support
📓 Project Summary – ✍️ Feedback and Suggestions – 📖 Game Wiki