alcaray: The installer has options for English, German, French, Polish, Portuguese, Russian (I think), and some kind of Chinese (I think). I did not try them so I can't confirm their completeness nor accuracy.
TheKaoBln: Hello,
the gog installer is not the same as the game. Since a few years the gog installer installs in many language but for a few games the installer let us choose languages in the options (but the most games are setable from ingame menüs).
btw the game has at this point no modern translatable engine. Pure Unity with no extra tranlating engine. I set 10 cents that this game will never multilanguage;).
It's true I've never played around with the GOG installer language option since I only know English very well. So I bow to your superior experience.
I did a check of their Kickstarter page for this project (Copper Dreams) but I could find no mention of localization. I tried the
https://whalenoughtstudios.com/ website but that seems pretty sales oriented and there wasn't a forum. They do list a contact email at the bottom of their home page, so you could send them a 'mail and ask your question directly if you wanted.