In the Esperanto language community he is known as the co-author of the relevant Esperanto grammar and as the initiator of the main monolingual dictionary in Esperanto, the Plena Ilustrita Vortaro. In 1948 he gave the letters of the language founder Ludwik Zamenhof Lejzer commented out. He also wrote a number of articles and essays on literature and history of this language.
- Parnasa gvidlibro ( with Kálmán Kalocsay ), 1932
- Plena ( analiza ) Gramatiko ( with Kálmán Kalocsay ), 1935, 1938, 1981
- Leteroj de L.L.Zamenhof (Editor ), 1948
- Lingvo kaj vivo ( essays ), 2nd edition, 1989 ( 1959)