To Yeelight uses who live in Germany,
We planned to build German language in Yeelight 3.0, however, we don’t have enough resource to do it. Today Yeelight 3.0 released without German builtin.
We plan to integrate German in next update, now we need your help to translate. If your have interest, please contact me.
Thanks,
Andy Ding
Could you upload your translate strings to crowdin or similar service so everyone could help translate to whatever language?
Hello Andy,
I’m a satisfied Yeelight-User from Germany and would be happy to help translating the yeelight app for the next update. I couldn’t find out how to send you a private message here, but I see that I can reply to messages i get. So you can contact me via PM 
best regards,
Michael
Hello,
I’m from Germany and would be happy help you translate the app into german, if you could forward in instructions in how to do it to me.
Best regards,
Markus
Hi, I’m from Germany and would be glad to help you!
Best regards,
Marc
sind nur noch etwa 200 zeilen code. das meiste hab ich durch. 
geht aber im augenblick beruflich nicht. 
sonst hätte ich das letzte stück auch noch übersetzt.
Hello all,
i found an old yeelight version translated in german. I tested it and it works but it was not updated since 01.02.2016 so the app is missing a lot of features. But maybe it helps you to develop an ofiicial german translation. I am really looking forward
Hi everyone, if your have interest to help us with German language, please contact me. Many thanks!!!
Have found a very nice person, thanks for your support!!