Twice so far.

Proprietary language to commonly used language - Got something on my CV that other future employers would appreciate more. Also was a chill job anyway. But I got bored.

Then I hopped jobs to another completely different commonly used language (not just different in syntax, but one that required a completely different way of thinking about things). I learned a lot, but project itself was way too stressful, so I quit at the end of my probationary period. Not a good outlook on my CV, but overall I can, without lying, say I pick up on new languages and frameworks very quickly and if I get a take-home assignment in a language I’ve never touched, I can still complete it in a reasonable time frame. So there’s some good out of it.

Both times also came with a significant salary increase so that’s also nice.

I’m withholding details about the languages because I might be too easy to identify given I’ve also mentioned my homeland in previous comments.