As one who studied a non-core language full time for over a year to gain 3333 level - I can tell you it's very, very hard work (and I scored well on the MLAT). Moreover, a huge amount of time is needed to maintain any degree of fluency, and this is principlly achieved through immersion training (no, not that sort...). And that was just so I could attend the local Staff College Advanced Course.
The FCO will send their people to live with families in difficult-language countries for up to 18 months, whilst they attend local courses. Can you imagine the MOD funding that for your average SO3/2 who is not in a language-related post?
If the Army is serious about this, they have to accept that the training has to be full-time for about a year in most languages; 2 years for Asiatic, Turkic and Arabic languages. The DCLC exams need to change, too. They are all predicated on the student leading a patrol in Helmand (irrespective of the language). 'Did the attackers leave on bicycles?' being a particularly memorable phrase for me to learn during my language training.
Edited to add: this is all about the Army making their Brigades as indispensible as possible. A while back I attended a number of briefings by 'Joint' and Army-led units. It was all about showing how vital that particular unit would be after Herrick (AFG).