Okay, first off, AKs are all over the world because Russia and China distributed them to revolutionaries and socialist governments for four decades. Yes, given a choice, they would probably choose different weapons, but the fact is, when you can't afford or even get your hands on anything else, a knife is better than nothing in a fight to the death.
As for your Special Forces, (Wait, France has a military? When did that happen?) if they are anything like U.S. Special Forces, they train with foreign weapons because they may be inserted behind enemy lines, linked up with insurgent or even anti-insurgent groups, and you have to be able to use what they have.
Are AKs accurate? Most people I've talked to say yes, out to 100 meters, but I have a .357 mag lever action, and as long as I adjust the sights for range, I can get the same level of accuracy. Full auto, you're lucky to hit the broad side of a barn at 50 paces. Are they reliable? As far as can they shoot if not maintained very well, yes they are reliable. If you want to talk about how long they will hold up, then no. The parts are machined by low-skilled workers with a weak grasp of things like quality control, metalurgy, or precise tolerances, which is why they will fire when dirty. But that also means that AK parts wear out faster, and when they fail they will blow up right through the stamped sheet metal receiver.