The fragment catalogued as a “German sermon or theological treatise” is a verse-by-verse German exposition of Isaiah 52:13–53:12, 15th century.
Acknowledged: The holding library has said the identification is new to its records. That is not peer review. The library said the identification was new to its records. Whether the text itself is new is an open question.
The language is Bavarian-Austrian. Its reading of 53:9, the Jews given over to the Romans, is found in Haymo of Auxerre and the Glossa tradition. No German parallel has turned up, but German exegesis of this period is poorly searchable, so absence of a parallel proves little.