He spoke Esperanto from childhood and used it in Japan, China, Uzbekistan, Kazakhstan, in Africa and Latin America, and in nearly all the countries of Europe.

His French-language book Le défi des langues — Du gâchis au bon sens (The Language Challenge: From Chaos to Common Sense, 1994) is a kind of psychoanalysis of international communication.

In a lecture on the current system of international communication[1] Piron argued that "Esperanto relies entirely on innate reflexes" and "differs from all other languages in that you can always trust your natural tendency to generalize patterns...

is a novella which uses basic grammar and vocabulary in the first chapter and builds up to expert Esperanto by the end, including word lists so that beginners may easily follow along.

He argues strongly for imaginative use of the basic Esperanto morpheme inventory and word-formation techniques, and against unnecessary importation of neologisms from European languages.