Scala doesn't make a distinction between operators and methods, and Java has always supported unicode in method names, so they have to be possible for compatibility if nothing else. I think if used carefully, with discipline, they can make code more readable and ultimately more maintainable - e.g. for doing set algebra it's nice to be able to have ∪ and ∩ methods. But yes, if you want to shoot yourself in the foot with them it's very easy.

Perl6 also has unicode operators - https://news.ycombinator.com/item?id=4942377