[Const-me]

For some of these things we don’t have much choice, because the encoding is part of some lower-level API (file system, OpenGL, CLI), which usually don’t accept arbitrary encoding. They accept only one, and unless you want to waste time converting, you better use that exact encoding.

Other stuff like IDs, shaders before GL 4.2, and many text protocols aren’t Unicode at all.

For configs I usually use UTF-8 myself, because I don’t like writing parsers for custom formats and just use XML, and any standard-compliant parser supports all of them.