Mine is a problem that seems simple but is actually complex. I played the whole campaign Dragonfall (I have the Director's cut), I later discovered that, between the campaigns installed, there was also DMS.
I then followed a guide to install DMS directly into Dragonfall (so it takes up less disk space), and everything went well.
That said, I had to play in English Dragonfall, but DMS is also available in my language, only that Dragonfall refuses to change language.

I did a little research, it seems that on the windows is enough to change a registry key (Setting.Language from None to the capital letters of the country) but I'm on mac.
I still found the equivalent of the register, unity.Harebrained Schemes.Dragonfall.plist, which has a value Setting.Language None, but if I change it, as soon as I start the game, it returns the value None.

I think at this point I'll play everything directly in Shadowrun Returns (at least DMS).
What I wonder is, the developers have forgotten that the mods can be in different languages?
Someone has managed to change language (with another procedure)?

Thank you.

For that I'm read in forums were are trying to translate the game, when you start a new game, its start in English, but if you save the game and reload it, it loads in the selected language.

I tried that solution. it does not work on mac (or maybe I do something wrong I don't know...).
the problem is... with shadowrun returns I can change language in-game, the interface change language, the campain change language (if the campain is not in italian it start in english)... with shadowrun dragonfall you cannot change the interface language so you can only start a game in english... a friend have the old shadowrun returns + dragonfall DLC with that version he can play both campain with italian interface but with dragonfall in english.
I think that if I could replace the english localization file, I could just let the game think I'm still using english... but the localization files are .mo.... and there is not an en/eng folder with .mo.... only .mo on the other localization languages (so no english at all and I don't know where the game read english text).

thank you anyway.

I confirm, it work's on Windows ! ;)
The key is localized here : Computer\HKEY_CURRENT_USER\SOFTWARE\Harebrained Schemes\Dragonfall

Thanks for the tips ! :)