Very interesting. I do believe that below a certain level of native French speaking recruits, this can have adverse consequences on the operational level of the Legion. For the foreigners, if you can quickly demonstrate you have a good mastery of the French language, that will definitely be a plus, if you want to make a career in the Legion.
I saw the other day a documentary on the Legion (yes... another documentary), that I had never seen before. It was shot in 2006 by Elizabeth Nord, a Norwegian TV producer, at 2e REI in Nîmes. It was broadcasted on French channel RMC in three episodes of one hour each. Apart from the fact it was for me an opportunity to see again my old friend Calmon (a Lt-Col at that time), the documentary was quite interesting (i.e. not too much ‘propaganda’) in that it didn't avoid some difficult topics, like desertion (actually, one of the legionnaires interviewed in the documentary, an English, deserted during the shooting). One of the cadre who was one of the recurring characters was another English, a NCO and platoon commander with 20 years seniority in the Legion, Adjudant Raubenheimer. He clearly said that, being able to speak (reasonably) good French was important if a legionnaire wanted to progress. To help them, he said he made a point talking in French to all the legionnaires in his platoon, even the English speakers. He also criticized one of his men, a Slovak, for not making enough efforts in improving his French, in particular because he spent all his free time with his fellow countrymen talking their native language. The Adjudant basically said, even if the legionnaire had potential, not speaking good enough French was a clear hinderance to his career..