After a little more than a year total of living and visiting in Mongolia, my current knowledge of Mongolian is probably about the level of a smart 3-year-old toddler who just happens to know how to read very well (the Cyrillic version, not the older script). It's enough to get by at the store, reading signs and labels, and for simple requests, but not enough to get by in actual conversation (hard to converse if you only understand 1 out of every 5 or so words). No actual language lessons or classes, just immersion, self-study, and some help from my wife and her family. It's not an easy language, but certainly not as challenging as learning Mandarin in my opinion. I've never had much talent at learning foreign languages, so some people would probably learn faster than myself in similar circumstances. If I took formal classes I'd probably be further along, but that's not easy with my schedule.
While it is hard to operate in Mongolia without the language, I have noticed in just the past 4-5 years much more of the younger generation in UB showing some limited knowledge of English or even full proficiency. It's not anywhere to the point that you can rely on someone knowing English wherever you happen to be, but it has turned out to be a useful time-saver on occasion. Maybe the next most common second languages here could be Russian (mostly the older generations) and Korean, with a small number knowing some German or even Mandarin. In my limited experience Mongolians in general seem to show a good aptitude for learning new languages, so who knows what it will be like a decade from now. But for now, operating in day-to-day life in Mongolia without the language is quite difficult. So if you don't know the language and you're doing business here or especially working with the government, you likely will need the services of a translator at various times.
