I am sorry but "I learn" is awkward English. I understand that dang is used for present continuous in Vietnamese, which I assume is taught later in the tree, but in translation for English, it is almost always present continuous so both "I learn" and "I am learning" should be accepted. I cannot think of an example of "I learn + skill". "I learn fast" or "I learn quickly" maybe. You can say "I study History" but this is implying like what your focus of study is in university.
Because Vietnamese people naturally drop the 'đang' if it's implied in the question (at least in my experience, Hanoian Vietnamese), also because we use present cont. in English to describe learning skills even when not currently doing them, I think 'I'm learning Vietnamese' is equally correct here.