Dave,
www.military.ie should spell it out in the careers section. From what I understand the foreign language was included in the 'minimum education requirements' to mirror most CAO courses which had a similar requirement. In that respect it could be aimed specifically at school-leavers as opposed to college graduates. I recall the education part of the career booklet contained a phrase along the lines of 'leaving cert inc three higher Cs and three passes to inc a modern european language OR a standard of education the minister deems suitable.'
A college qualification is a higher qualification than the leaving cert so whether or not you have a language at L.C. level might not matter.
That's my two cents anyway but try the above website, at the very least it might have a direct contact to the employment officer.