From a career perspective, working in one single language seems far more limiting than focusing on some esoteric language(s). I don't even understand how it's possible to spend five years in one language. On a day to day basis I use JavaScript, bash, and python.
Focusing on only C++ or Java or one of the "mainstream" languages seems just as "bad" as focusing on one esoteric language. Try to pick a job where you are exposed to multiple languages/paradigms on a daily basis.
In your cliche NET 2.x MS-only Windows-Only enterprise setting they won't look down on it, but they might feel you don't have relevant experience.
In many other places people value developers that have non-mainstream development experience because it shows you're willing to explore as a developer and won't shackle yourself to one solution to problems the business faces.