Does this make letters of recommendation from German companies meaningless?
Some will say yes, but regardless of that, what is certain is that the whole situation developed a kind of flourish language that can express at lot about the employee without ever being obviously negative. Some sentences can even be translated into school grades.
There are numerous books about this language and even more websites and they all more or less agree, so this language is pretty standardized since at least maybe 30 years. A last interesting point about this language is that some things are said by leaving out certain phrases or words, so you say something by not saying something.
Finally I'll give you few examples [+]. May they serve as an example for a future AirBnB language;-)
He has specialist knowledge and a healthy dose of self-confidence.
Meaning: This person is an arrogant jerk.
He's quickly become popular with clients.
Meaning: This person can't negotiate at all.
She had great empathy for the needs of the staff.
Meaning: This person flirted more than they worked.
His sociability helped to improve the atmosphere a work.
Meaning: This person is an alcoholic.
[+] Translated by me to the best of my knowledge. I'll spare you the German originals to avoid clutter. If you want sources shoot me a message, E-mail is in my profile.