Earlier quoted context omitted.
JavaScript has virtually always supported Unicode variable names (well, the basic multilingual plane). https://mathiasbynens.be/notes/javascript-identifiers
Sure, but do people in general use them?
Although compression tools replace the majority of symbols with short Ascii symbols, so it may not show in the final packed code.
It looks like the closure compiler emits Ascii only, using escapes for Unicode symbols that are not transformed.