> But if you know 2-3 closely related languages, one that isn't closely related to those 2-3 can be problematic.
Indeed. Not sure if you left it out on purpose, but my comment included (right after the part you quoted) the following: "(except the really different ones)", which covers exactly what you're talking about :)
I mean, if you know 2-3, say, static class-based OOP languages, other static, class-based OOP languages mostly look/work the same.
If you know 3+ languages with wildly divergent paradigms, you can probably pick up most new languages even if they don't look/work the same.
But if you know 2-3 closely related languages, one that isn't closely related to those 2-3 can be problematic.