Hello there!

I really like GOG Galaxy app and I want translate it to the Czech language, because this localization still missing.

It´s any possible way, how can I do that ( for example using Transifex ...)?

It could be possible.
I downloaded GameExtractor program and extracted en-us.pak from C:\Program Files (x86)\GOG Galaxy\locales directory.
I extracted them to extracted folder but the file name and extension was .unknown. There are some .empty files which are just empty files.
I made batch file that renamed all .unknown files to txt so it can be edited in notepad.

But i dont know how to put it all back into .pak.

Here are those files in zip: https://www.dropbox.com/sh/zvgrbfxf4ag64qw/AAAOtFPyG_hblItRkcBPTv-Na?dl=0

Cyberpunk 2077 has stupid bug:
1) when you set language to Czech
2) next time is game again in English !?!