What problems do teeangers with immigration background have in Austria or Germany?

Depends on where they are from.

Moslem immigrants to Germany (and for that matter, much of Europe) have tended to stay within their communities (and not attempt to mix in the broader German culture). For whatever reason – partially religious, partially family – they have chosen to live separately from the mainstream German population.

That, in turn, causes the mainstream German population to look at the self-contained Moslem population with suspicion, since the Moslems don’t appear to share common goals, beliefs, outlook on life, etc.

So to a degree, that group of immigrants, by not attempting to mix with the greater society, has put itself under scrutiny. And that makes life difficult for immigrant youth.

(note: this is not just Germany – it is true in the UK, in France, in Sweden, in Norway, and so on.)

Mostly language related problems.
If you do not speak German, you will invariably have problems keeping up in school, which in turn lowers your carreer options later on.
Needless to say, university becomes nearly impossible, because besides requiring the Abitur, there are minimum grades you need to have to be accepted.
Even companies looking for trainees require at least an average school performance.
Some, such as the banking industry, even go so far as to require Abitur, which was historically only the prerequisite for enrolling in a university.