I like learning languages (Esperanto, German, Chinese, Japanese), but consider it as more of a hobby than a useful skill, unless you're planning to move abroad, or have a job that involves a lot of travelling, or marry someone from there.
More useful than video games, reading fiction, surfing on reddit, playing chess.
Less useful (marketable) than programming, self-marketing, public speaking, fixing up your house, negotiating a salary, driving a car, fixing a car...
Probably about as useful as drawing, or doing advanced maths.
What exactly do you mean by "marketing" in this context? Marketing in a business sense is not something I'm familiar with people learning as a self-taught skill, and I'm not sure how seriously employers would take it, but self-marketing as a general skill is broad enough to seem like the odd one out among those options.
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.