[realharo]

>Firstly, people simply don't apply for jobs that use languages they don't know.

That could be because experience with that language is often listed as a requirement.

>someone spend the first few months getting up to speed

In my opinion, "few months" is a huge overestimation, if we're talking about an otherwise experienced mobile developer who understands the underlying platforms (Android, iOS) well. A few weeks should be enough to get up to like 90% of their usual productivity (ballpark guess).