I cloned git.savannah.gnu.org/r/emacs.git and built emacs. I set the HOME envvar to ‘D:\Marci\Programozás\emacsdebug’ which contained the repro case from above. I still get wrong output when the load path is printed:

Loading d:/Marci/Programoz  s/emacsdebug/foo.el (source)...

"d:/Marci/Programozás/emacsdebug/foo.el"