Arabic language in the Book of Mitzvot and Roots by Rambam

The rabbi wrote in his book 'The Spirit of Justice', page 24, by way of hypothesis that the Rambam wrote the Book of Mitzvot and Roots in Arabic so that everyone could be convinced by his words.
In his letters he says this explicitly (Shilat edition, p. Rechba) and the late "And I was greatly comforted by the fact that I composed it in Arabic, because everything needs to be read …"