We used to present a variant of the main German stemmer, termed "german2" which was the same as the German stemmer but adjusted the first step to improve handling of input text where the German letters ä, ö and ü, were written as ae, oe and ue respectively.
Snowball 2.3.0 added these adjustments to the main German stemmer, so there is no longer a "german2" variant - just used the "german" stemmer.