Support localized number format in question text

[PhilippImhof]

Originally posted by @marlisschedler in #11

They see numbers like 3.5 in the question text, even though they are taught (and now allowed!) to write 3,5. This inconsistency between display and input causes confusion – especially because my learners are 10–14 years old and don’t use tools like Wolfram Alpha or programming languages where the dot is common.

So my wish would be: a way to format numbers in {=...} expressions maybe based on the language pack (e.g. de, de_du

When implementing this, it would make sense to also apply it to the feedback and particularly to the "correct answer" feedback.