Everyone please post in English outside of language pack discussions, as per our community guidelines. Not everyone can follow what is being discussed otherwise.
ctupramod I guess something went wrong in between the beta and the stable
Many changes were made, often to improve performance. This was certainly not done on purpose. But I doubt we will find any single change that's responsible for this, it's probably a group of changes that caused it.
If anyone has technical insights on what needs to be changed, please add your findings to our GitHub issues. We have a GitHub issue summarizing most of the unicode-related issues here flarum/core#2230
Once that's fixed, some integration tests should definitely be added with example search queries in various languages to ensure this doesn't get reverted again.