Hello,
I'm making a czech localization of unraid. It's still very much work in progress, but I think it's ready for public testing.
The translation currently resides in my github repo at https://github.com/Pavuucek/unraid_lang-cs_CZ. Just download a master branch snapshot file https://github.com/Pavuucek/unraid_lang-cs_CZ/archive/refs/heads/master.zip and install it via Tools/Language. You need to enable developer mode first.
Please report any issues you may find either here or as an issue on github (link above).