Complex sentence: Together with Dimitri Frenkel Frank Long composed the Dutch version of the musical Chekhov, which was a big success in the Netherlands, but the German version in which Long also participated, was less popular.
Split into simpler sentences: Together with Dimitri Frenkel Frank Long composed the Dutch version of the musical Chekhov. This musical became a big success in the Netherlands, but the German edition where Long also participated in became less popular.