Sleumer began learning Volapük only in 1892—after the "classical period" of the Volapük movement, directly from Schleyer. In 1910, Schleyer named Sleumer his successor, and when he died in 1912, Sleumer became Cifal. In 1921, Arie de Jongproposed to Sleumer his plan for reformingthe language, and when this reform was prepared in 1929, he put the whole not only to Sleumer, but also to Jacob Sprenger. Sleumer, De Jong and Sprenger were the last group who led the linguistic development of Volapük like a small school. In 1934, Sleumer issued a decree regulating the rights and duties of Cifals; in 1948 he resigned as Cifal, appointing Jacob Sprenger his successor. Sleumer was a famous Latinist and theologian, defending in 1906 the need for the Church censure.
Works
1914. Ein berühmter katholischer Erfinder. Ein Lebensbild. Volksaufklärung, n. 180. Klagenfurt: St. Josefs-Vereins-Buchdr.
1926. Kirchenlateinisches Wörterbuch.
1935. "Volapükamuf bü tumyel lafik", in Volapükagased pro Nedänapükans, Nüm: 2, Pads: 9-14.
1938a. "Pük menik", in Volapükagased pro Nedänapükans, Nüm: 6, Pads: 44-47.
1938b. "Daved Volapüka", in Volapükagased pro Nedänapükans, Nüm: 4, Pads: 26-30, e Nüm: 5, Pads: 34-38.
1939a. "Hieroglifaston di ‚Rosette‛ in Dältad di ‚Nile‛", in Volapükagased pro Nedänapükans, Nüm: 1, Pads: 2-7.
1939b. "Bödaflen de ‚Joplin‛, ‚MO‛ ", in Volapükagased pro Nedänapükans, Nüm: 3, Pads: 28-29.
1939c. "Dö Mäsiat dobik e pats votik se rujenav relik", Volapükagased pro Nedänapükans, Nüm: 4, Pads: 36-38, Nüm: 5, Pads: 44-46, e Nüm: 6, Pads: 50-55.
1940. "Yesus Kristus in Kuraan Slamanas", in Volapükagased pro Nedänapükans, Nüm: 1, Pads: 4-9.
1949. "Kardinan: ‚Mezzofanti‛: pükinolan mu süperöl", in Volapükagaseds pro Nedänapükans, Nüm: 3, Pads: 11-12, Nüm: 4, Pads: 15-16, Nüm: 5, Pads: 19-20, Nüm: 6, Pads: 21-22.
1951. "Namapenäds e buks bisarik", in Volapükagased pro Nedänapükans, Nüm: 3, Pads: 10-12, Nüm: 4, Pad: 13.
1962. Deutsch-kirchenlateinisches Wörterbuch. 3rde edition of the edition of Ferd. Dümmler/Bonno on occasion of the inauguration of the Second Vatican Council.