I'm currently studying Finnish and Vietnamese (very different languages!); both will probably take me a few years to get the hang of even at a basic level, since I'm not hugely graced with a talent for languages. But there are lots of interesting facets even dipping one's toes into the water.
Vietnamese has a beautifully simple grammar. It's a tonal language, which means pronunciation is difficult for a native English speaker, but the tonal system itself is in reality not very complicated -- there are only five or six tones depending on the dialect, and they are fairly different. The (very) hard part is being consistent. One aspect of Vietnamese that is very difficult, though, is how it handles pronouns. How you address or refer to someone depends on their age and status relative to yours. And most of the 'pronouns' are familial. So, for instance, if you greet someone, with chào, which is more or less 'Hello', it matters whether the person is old enough to be your brother, your parents' age, or your grandparents' age.
Chào em, for instance, is for people definitely younger than you are. Chào anh is for men old enough that they could be roughly your age, maybe a little older; chào chi is for women who are the same. Chào chú is for men who are old enough to be a much older brother; chào cô is for women who are the same. Chào bác is for men or women who are your parents' age or slightly older. Chao ông is for men old enough to be your grandparents' age, and chào bà for women. It's built into the 'pronouns', really; anh actually means 'older brother' and ông means 'grandfather', for instance, so what you're doing is extending the same courtesy you extend your family members, with the caveat that the greater the age, the more respected the title, so when there's ever a question you should always err on the side of taking them to be older than they are.
It's a social system in a language. But it's quite complicated, especially when it intersects with status or real family relationship. Just from what I've seen, even native Vietnamese have some difficulty figuring out what to do if you have a son who is a priest, for instance: sons should be addressed as younger people, but priests should be addressed in the same way as fathers (or perhaps as grandfathers, since that is more formal). Technically, titles should overrule ordinary age considerations, but that's a very formal convention, which is awkward in a real family situation. It's equally difficult for the priest, whose title makes him a father (or grandfather) with respect even to his mother; but speaking in that way to one's mother would usually sound extremely disrespectful, and I doubt that there are many priests who would dare do it. In our age of mass media, another challenge has arisen: you are often addressing people whose age and status and sex you do not know. So in advertisements you often get addressed as bạn, which means 'friend'.