Horrific? You might not think so if your (human) language used a different alphabet.
Yes but also no. The thing about software is that 90% of it is not culturally bound. If you're writing, say, some tax reporting tool, a grammar reference, or something religious… sure, it makes sense to write that in your language. So, yeah, C should support that.
However, everything else, from spreadsheet software to CAD tools to OS kernels to JavaScript frameworks is universal across cultures and languages. And for better or for worse (I'm not a native English speaker either), the world has gone with English for a lot of code commons.
And the thing with the examples in that post isn't about supporting language diversity, it's math symbols which are noone's native language. And you pretty much can't type them on any keyboard. Which really makes it a rather poor flex IMHO. Did the author reconfigure their keyboard layout for that specific math use case? It can't generically cover "all of math" either. Or did they copy&paste it around? That's just silly.
[…could some of the downvoters explain why they're downvoting?]
Little to no source code is written for single (human) language development teams. Sure, everyone would like the ability to write source code in their native language. That's natural.
Literally no one, anywhere, wants to be forced to read source written in a language they can't read (or more specifically in this case: written in glyphs they can't even produce on their keyboard). That idea, for almost everyone, seems "horrific", yeah.
So a lingua franca is a firm requirement for modern software development outside of extremely specific environments (FSB malware authors probably don't care about anyone else reading their cyrillic variable names, etc...). Must it be ASCII-encoded English? No. But that's what the market has picked and most people seem happy enough with it.
My language uses Cyrillic and I personally prefer English-based keywords and variable names precisely because they are not words of my (human) language. It introduces an easy and obvious distinction between the machine-oriented and the human-oriented.