Let's say that I'm writing a library in C# and I don't know who is going to consume it.
The public interface of the library has some unsigned types - uint, ushort. Apparently those types are not CLS-compliant and, theoretically speaking, there may be languages that will not be able to consume them.
Are there in reality languages like that?
I believe in the original version of VB.NET, unsigned types were usable but there was no support for them built into the language. This has been addressed in later versions, of course.
Additionally, I suspect that the now-defunct J# has no support for unsigned types (given that Java doesn't have any).