I've brought this up on Trello and wrote PMs to PixelTail but that's the past of more than 2 years ago when I wasn't sure if I should make a topic about translation issues in general or just focus on this one but I guess one topic per issue seems reasonable. I haven't seen a decision already made on this and it's not relevant yet until localization becomes a priority so there's now time to calmly discuss the options:
In the German langauge, the "You" referencing a single person can be translated to "Sie" which is formal and polite but also "Du", which is more personal on a friendly level. I personally would suggest to translate TU with "Du" because TU is a place to have fun in with friends and be silly, not a job interview location.
Just to be clear: I'm opening this thread just to raise awareness of and discuss the issue and get a sense of what people would generally prefer.