Is your feature request related to a problem? Please describe.
The web site states: “Java code should be written with ASCII characters only, no UTF-8 support.” This is ambiguous. I suppose that it means at least that identifiers must be in pure ASCII, but does it also mean that all file content must be in pure ASCII? Can I use UTF-8 in //comments? Can I use UTF-8 in Strings?

In supplement of being ambiguous, it is a strong restriction, if it is meant in the wide sense of all file content being restricted to pure ASCII. For example, Google Java Style writes: “Tip: Never make your code less readable simply out of fear that some programs might not handle non-ASCII characters properly. If that should happen, those programs are broken and they must be fixed.”

Describe the solution you'd like
Please consider allowing UTF-8 in comments and Strings, and update the sentence referenced above accordingly.

If this is not considered possible / adequate, please change the sentence anyway to make the limitation unambiguous.

Additional context
From this discussion and this question, I suspect that Checkstyle already supports UTF-8 in comments and strings. So I suspect this feature request would be easily implemented. And it would bring important value to those who (like me) agree with the quote from Google Java Style here above.

Other (vaguely) related issue: #2784.