I originally owned the German version and purchased it and all the DLCs individually via Steam.
While on vacation in the US, I bought the ultimate edition (CD) and brought it back. The files worked fine and translated over perfectly.
The files are just that: basic files. Nothing about your character files locks them in or forces them to be played with a specific version. As long as you still have access to your original character files, you can open them with a Hungarian version of the game, if you wanted to.