Nope. If you read an ASCII file with control characters in Java you’ll get an exception. Also it won’t work with the 8-bit ASCII variants. Neither are “true Scotsmen” of course, but the point still stands that HTML could yet be more durable.
I’m almost certain the default encoding for reading/writing files in Java is UTF-8 and similarly for the source files. I don’t think I encounter wide char data much really at all day to day ...