[2022] Language does not work properly

Eco uses language on client and on the server, e.g. the two can have differing languages which means that the server displays server-side stuff in the language that was configured for it. You can change the language for the server in /steamapps/common/Eco/Eco_Data/Server/Configs/Localization.eco, just enter "German". If you're not the admin, you would need to ask the admin of the server if he is willing to do that.

Yes, server language and client language is different, that also enables you to add modifications server side with localization and change the name of recipes and basically anything server-side with simple measures. Things that are fully configurable / changeable / deletable on the server are served via it, not the client. It is nowhere an optimal implementation and that wasn't claimed anywhere either, but it does work as it was developed and is not a bug. It has advantages and disadvantages on many levels and we'll surely look into that again in the future, but for now it is working correctly.