How do you say "To take a gap year"?
I don't think there is a 'clear' translation because of the culture difference behind it. Chinese people don't take a gap year until very recently and the few who do are still considered rebel by many. It hasn't become that popular yet to have a well-known terminology. In some circles it's just called gap year, gap年 or 间隔年.
间隔年 is probably the best option for now, but you may still want to define or explain it to the audience beforehand. This translation has actually made its entry on Baidu Baike and appeared in a book title 迟到的间隔年.
You can see how some people still refer to the concept as 'gap year' in discussions like this, which suggests the Chinese term hasn't got its full popularity yet.
As for the verb ('take'), I think the best context-free translation is 体验 (to experience). Depending on the context you can also use 开始 (to start) or 要 (to have). E.g.

He decided to take a gap year after graduation. 他决定毕业后体验间隔年 (formal) or 他决定要个间隔年 (colloquial).
His friends took a gap year right after graduation, but he didn't. 他的朋友们一毕业就开始了间隔年，但是他没有。