As an Esperantist, Tonkin has written and translated numerous works in and about the language. Between 1974 and 1980 as well as between 1986 and 1989 he was president of the Universal Esperanto Association.
As an ardent supporter of Esperanto, Tonkin has created and translated numerous writings about the language. His leadership as president of the Universal Esperanto Association had a lasting impact on the language's development between 1974 and 1980 and again from 1986 to 1989.