Because if you speak only English and are surrounded by vast stretches of land on every side of you where people mostly only speak English, you don't feel the pain. (And seriously? One reason most code might be written only in English is due to the systemic bias of programming environments that only support English.)

I have seen a fair amount of non ASCII string literals. Multiple currencies, for example.

I assume utf8 has some problematic glyphs in this space.