In Armenia, the national language is Armenian, and the dialect is Eastern (or perhaps simply Yerevanian). Most can speak some decent Russian, and many speak a little English. Other languages are more hit and miss. The Western Armenian dialect is understood okay by many – especially those who descend from repatriation movements of the 1940s and 50s, those who work with tourists, and those with a better education who have studied Armenian literature of all kinds. No matter what your Armenian dialect, you’ll generally be able to communicate as you adjust.
If you speak no Armenian at all, there are plentiful tutors, books, tapes, etc. Many locals will be happy to practice their English on you while you practice your Armenian on them. American Peace Corps volunteers of all ages learn enough Armenian to get by and live in a village in a matter of weeks, so it really isn’t an impossible barrier for anyone.
Most jobs of course require fluency in spoken Armenian, but not all. Reading/writing is much less important. If you’re thinking about making the move however, there’s no question that you’d do well to start learning some of the basics as soon as you can.