Complex sentence: It was the fashion during Wunderlich's career for German theaters to perform operas in the local rather than original language, so most of his recordings of the standard operatic repertoire are sung in German, including Verdi's "Rigoletto" and "Don Carlo".
Split into simpler sentences: It was the fashion during Wunderlich's career for German theaters to perform operas in the local rather than original language. Therefore, most of his recordings of the standard operatic repertoire are sung in German, including Verdi's "Rigoletto" and "Don Carlo".