I'm new to the Fever series but I just fell in love with Transport Fever 2 and played it for hours since I got it.
In my play time, I noticed there were some untranslated strings in the french translation and from what I heard, in some other languages too.
So I just released a tool that lets everyone fixing existing translations or even rewriting one in another language.
It is called TF2 Translator and you can get it https://www.nexusmods.com/transportfever2/mods/3]on NexusMods[/url] as this kind of external tool have no place to be published on steam.
I hope it will be of some help for this overall extraordinary game.