I was not able to reproduce.

Without a ~/.freedroid_rpg dir, or without a fdrpg.cfg file in it, or with a
wrong content in that file, in any case the game started with my system locale.

Looking at the source, the game is initialized using the system locale, and only
if a locale definition is found in the config file do we switch to an other
locale...

So, I do not understand why it was not working for you.

Can you reproduce ? What is your system locale (please copy/paste the output of
the 'locale' command) ?