The most valuable qualities of a software engineer are language agnostic.
Great employers know this already but it’s worth reiterating: years spent writing in a language do not equate to quality as a programmer.
A seasoned Java developer who has never written a line of Ruby in her life is not inherently a worse candidate for a Ruby job than the next guy who has been working alone for all ten years of his career DRY’ing up every class like a chamois because no one taught him that there’s such a thing as a bad abstraction.
There are concepts to learn that extend beyond your current tech stack. Don’t get stuck trying to learn all of the hot new languages, learn to write better software and you can transcend whichever stack you’re surrounded by.