Complex sentence: Frölich is best remembered as a pioneer biographer of the assassinated Communist Rosa Luxemburg, with his book on her translated into a number of languages, including Spanish, English, French, Italian, Slovenian, Korean, Greek, Hebrew, and Japanese.
Split into simpler sentences: Frölich is best remembered as a pioneer biographer of the assassinated Communist Rosa Luxemburg. His book about her has been translated into a number of languages, including Spanish, English, French, Italian, Slovenian, Korean, Greek, Hebrew, and Japanese.