Brendan Francis Aidan Behan (christened Francis Behan) ( ; Irish: "Breandán Ó Beacháin" ; 9 February 1923 – 20 March 1964) was an Irish Republican, poet, short story writer, novelist, and playwright who wrote in both English and Irish. He is widely regarded as one of the greatest Irish writers and poets of all time.
Behan wrote stories in French
The context says he wrote in English and Irish, but it doesn't say he wrote ONLY in English or Irish.  It is possible that he may have written other languages, given the context. 