Actually, that’s not true. For many software developers, it is an ASCII world. But, if you’re making software for other developers to use, please keep character encodings in mind. I’ve had to jump through hoops with many packages along the way to get them using UTF-8.
Luckily, when you use open source libraries, the lack of non-ASCII support is usually not a big problem, because it’s easy enough to add the support. Not so with a closed-source third party library. Though, anyone offering a commercial library would have to deal with encodings once they start offering the product internationally.