Pretty much anyone coding in another language. Coders do sometimes buy fonts if they are into fonts and nice terminals.

To reiterate the original question: "what percentage"?

What do you think are "random obscure glyphs"? Is the Turkish lowercase 'i' (ı) one of them? What about the German Eszett (ß)? Is 'ö' a random obscure glyph? What about 'ø'?

Yes, those are obscure and unlikely to naturally show up in monospace texts.

What percentage of computer programs do you think are written in turkish?

Sorry, the question was actually rhetorical: those glyphs are in no way obscure, they're super common. A text isn't monospaced or not, a text is just a text, monospaced is a property of a typeface that can be used to render a text, it's adjacent to other properties of typefaces like serif or sans-serif. When you dismiss stuff like ü or ø or ß or etc. as "obscure" (and, transitively, irrelevant) it comes across as ignorance.