I used to do my interviews in C++, but then I got burned during a Google interview when my interviewer talked about the inefficiencies of emplace_back vs push_back (I had no idea). After that point, I just decided to do JS because I was reasonably proficient at it, and it is actually faster to write than C++ in a lot of cases (less boilerplate).
The top LeetCode answers / YouTube explanations and such are usually in Java or Python, so sometimes it's also hard to find a good JS answer. I'm leaning towards Python, because it is more like JS and with less boiler-plate like Java, but I'm worried about something throwing out some random trivia about Python that I have no idea about, because honestly I haven't used it much in my career thus far.
From most important to least important, here are the criteria I'd consider wrt to language choice:
The above criteria is true for almost all Big Tech jobs. Interviewers here are trained to be language agnostic since the company uses dozens of technologies. (If you interview at a consulting shop, they'll likely be much more strict about what they want. These companies also pay significantly less.)
We touch on this in more detail here masterclass about DSA interviewing so I'd check that out! Also check out Daniel Tomko's advice about interview prep here.
Going into the issue further, here's the breakdown I've seen:
If you're more interested in what the other side looks like, we actually gave a masterclass about it (heavily inspired by my experience back at Meta). You can watch it here: [Masterclass] How To Be An Amazing Interviewer In Tech