B. H. Brown debunks in  the myth that "Algebra was Hebrew to Diderot" (cf. E. T. Bell, Men of Mathematics, NY, 1937, pp. 146-147).
Gillings mentions in his note that it is D. Thiébault's account the only authority in the Euler-Diderot anecdote (even though "Thiébault himself was not convinced of the truth of it...").
It is important to add that in Thiébault's telling version of the story there is no explicit reference to the name of L. Euler.
 B. H. Brown. The Euler-Diderot Anecdote. Amer. Math. Monthly. Vol. 49, Issue 5, 1942, pp. 302-303.
 R. J. Gillings. The So-called Euler-Diderot Incident. Amer. Math. Monthly. Vol. 61, Issue 2, 1954, pp. 77-80.