A Chinese translator reported an error when saving translations. The translation is saved properly but this makes for a very bizarre user experience. The resolution of the problem can either be tracked with the upstream bug report and an update will be posted in this thread when it is resolved.
It turns out this is a case of full text index corruption that can trivially be fixed with:
sudo docker-compose run weblate rebuild_index --all --clean
Let see if that happens again before trying to understand why and how to properly handle that kind of problem. The workaround is good enough for now.