Murray is a bit dated since he signed up in 1960. Today the "kinder and gentler" FFL has formal classes in rudimentary French, both military and common, for non-Francophones while they are at Castelnaudary. As much as possible engages are buddied up with a French speaker in the section who helps during initial training. But one must also learn on one’s own in order to become proficient.

However, as Tom points out, le Caporal-chef will expect you to understand his orders tres rapidement, or there will be consequences desagreables. At a minimum you must quickly learn to be able to properly report to the company commander:

Engage volontaire Rollet,
Trois mois de service,
Premiere compagnie,
Section de Lieutenant Danjou,
A vos ordres mon capitaine.

Sloane's The Naked Soldier is one of the better memoirs of the FFL in recent times. Many books have been written by deserters who obviously have it in their best interest to paint the Legion in as poor a light as possible. However, Legionnaires are never accused of being either Boy Scouts or saints.