Hi Sebastian,
Thanks for the clarification (that's what I thought you meant) and sorry for the delay--we had a long holiday here in the US.
As you discovered, the system won't go back and regenerate existing activity feed updates as in the case you described above.
Once you change your language however, any subsequent automatic feed updates will appear in the new language.
So in the case you described, all existing feed updates remain in EN but all those generated after you switched to DE will be in DE.
You can see how regenerating every automatic update every time a user changes their log on language could pose a serious, and unnecessary drain on system resources.
Regards,
Angela