Complex sentence: Lesser discovered five speakers of Kitsai in 1928-9--none of whom spoke English--but working through Wichita/English bilingual translators, he filled 41 notebooks with Kitsai material.
Split into simpler sentences: Lesser discovered five speakers of Kitsai in 1928 and 1929, none of whom spoke English. Communicating to the Kitsai speakers through Wichita/English bilingual translators, he filled 41 notebooks with Kitsai material.