British English. Funny because my pronunciation is American. I pay close attention to cultural differences (napkin/serviette & c.)
Diëresis. Yes, I spell it that way so the word is kinda autological.
Numbers in word form.
Reformed names. Qazaqstan, Eswatini.
Ligatures. I use ’em. For instance, in the word æsthetics. I do not use the massachusett (ꝏ) because it is heavier than having oo, when the entire point of ligatures is to minimise the heftiness of letters. And what if a word that starts with Oo begins a sentence?
“Ћ” for “the”. Currently beta-testing on my website’s home page. The hardest bit is that there’s no keyboard key for it.
&. I consistently use the ampersand inconsistently.
Words with Slavic origin. If my ear hurts when hearing one, I fix the spelling and pronunciation. For example, Weird Al Yankovič. The spelling doesn’t change much, while the sound becomes pleasant.
Language purity. While English is a combination of every language in the world, I am much more pedantic with Russian and Italian, where I don’t use loanwords unless they benefit the language.
Et cetera. Ah, Latin. The only logical abbreviation is “& c.” because “et” is not a word in English.
Single-letter Roman numerals in numerical lists. I use this to save space & time. X for 10, L for 50, C for 100, D for 500, M for 1000.
Four-digit numbers without comma between digit groups. It is fairly easy for the human eye to see that 1504 is one thousand five hundred & four and not some other number.
Month name ahead of days. Despite preferring British English I write December 8th, Sep 1st. There’s nothing wrong with the 4th of July, but the preferred form saves space.
Three-letter abbreviations for months and days of the week. Jan–Dec, Mon–Sun.
Titles in sentence case. Well, See, This Doesn’t Look Very Appealing, Does It?
“Internet” with the first letter lower-case. It’s not the 90s, after all.
Umlaüts. I don’t use them because English isn’t German. Therefore, it’s the Mœbius band.