Then they are quite bad developers, because that is exactly what a team of ours did in a two day hackacton.
Some learned C++ on the Arduino, some went with TypeScript and Angular, others with JavaScript and AWS Lambdas, together we got a robot arm to pick and drop pieces with a Web dashboard and remote control, talking with each other via the "cloud".
Naturally all of them had several years of coding experience, but in other languages.
It's definitely going to vary according to your familiarity with other languages in the family.
I came into a C# shop late last year from never touching C# before and was writing more or less idiomatic C# very quickly, but I've worked with lots of semi-colon languages so this is mostly familiar territory.
On the other hand if you've never seen a Lisp before, ten years of C++ and VisualBasic won't prepare you to get anything much done in Scheme. Your reflexes are all wrong, and that's going to take some unwinding before you're productive.
Also, people will hate it if you oblige them to use language A they don't know and which is poorly suited to the problem when they know language B that's well suited. Even if you've got a sane business rationale (e.g. bus factor, they're the only person who knows B in your organisation) they're going to spend a lot of time moaning about how terrible it is at this job they could do better.
I do not like C++ but I'm immediately dubious about whether I'd rather try to control a robot arm from Javascript. Is there an option where I just have my foot surgically removed by people who know what they're doing? I guess maybe if the robot manages most of this itself and I'm really only overseeing it the Javascript is less awful, but if there's an actual real time control loop I feel like I'm very much between a rock and a hard place.
