Google SWE interviewer here. You can absolutely interview in Ruby. I have it listed on my language interviewing skills page. It is harder to schedule for more obscure languages because we have to find 4 people with that language who are available.

This is the key insight. The company seems to be language agnostic - the pool of interviewers isn’t.

I was told I could use C# as that is the language I use the most. Thing is, I'm going to use Python anyway. If they're going to whiteboard me, I want a language that is easy to write on a whiteboard and, to me, Python would be that language. Besides, I'm over C#. Would love to program Python for a while.

I have interviewed with Google 7-8 times over the past 3-4 years (Google has mostly rejected me, but last time I cancelled the process with an onsite scheduled due to personal reasons) - every single time, Google has let me interview with JavaScript.

why do you keep re-interviewing? Is it for different roles?

Dude really wants there.

Google offers are some of the best for putting pressure on other companies.

I am currently at another FAANG though, and may not leave my company ever, even if it would likely up my compensation.

I interviewed and passed at google. Through 6 interviews I used JS, C, Go, and Swift. One of the tougher Qs was to make a pretty full-featured promise library from scratch in whatever language I wanted in one of those interviews. Chose Swift because I'm a fan of the syntax for blocks (esp when whiteboarding). Feedback was that was my best interview of the day. My experience - they wanted to know I could program, didn't care about language.

You wrote a promise library in Swift on a whiteboard? What?

How large was this whiteboard?

What is a promise library? Sounds rather complex, how does that even fit on a whiteboard?

It’s a js async idiom.

I interviewed in JavaScript, so that's not strictly true. And if you're interviewing for an iOS role, Objective-C is obviously going to be a hard requirement. But if you say Python then write Ruby in the actual interview, would they really care that much? (any Google interviewers care to answer this?) I gave JS as my primary language but did one of my interviews in Python because I felt like it - the interviewer was fine with it.

I just did an interview in Go. I think people have done javascript too.

Sounds like a miscommunication happened somewhere. You should provide feedback to your recruiter.

Maybe that's your experience, but there are a number of people that didn't have that experience. I mean, you think Google isn't going to let you use a language they invented in an interview? Maybe your interviewer was a jerk, or maybe this was for a very specific role in which only those languages are applicable, but almost all jobs at Google are generalists.