Damn, I don’t have an answer, but that’s a fucking great question. I had just assumed it would be the case, but never thought to ask about it.

There are a few ways we do it in Chinese.

In mainland, people would sometimes just type the initials of the pronunciation of the character. For example, hhhhh (哈哈哈哈哈, hahahahaha), sb (傻逼 sha bi, dumbass). It can get out of hand for people who are not super familiar with their vocabularies (like me, a Hong Kong Cantonese speaker)

Alternatively, one can just use a different dialect/version of Chinese. In Hong Kong, we can have both written Chinese and spoken Cantonese mixed in the same message. We simply pick which one of them gives a shorter version of the word. For example, 回家看看有無撞其餘活動 ([Written] Go home and see [Spoken] if it conflicts with other events). Sometimes we even mix in ancient Chinese.

First things that comes to mind: Japanese for “to laugh” is 笑う “warau”. The equivalent of “lol” then started as 笑. Over time it evolved into just the first Latin letter “wwwww”. Which kind of looks like grass. And because Japanese people love word play, logically the next step was 草 “kusa” - which means “grass” and now also “lol”.

Anyway, sentences in languages that use logograms, such as Japanese, are generally shorter since they just use one character where languages that use Latin letters need several (“Want to hang out tonight after school?” - 授業後今晩遊ぼう？). So standard text message character limits are plenty to convey A LOT of stuff in Japanese. (EDIT: See comment below about the quality of that Japanese sentence lol)

You can make sentences more compact if you want to: 今晩　遊？ is not a complete sentence but the essential parts that carry the meaning, “this evening” and “hang out”, are there so if you’re in a hurry that’ll do.

Going further back in time might be more interesting, the Japanese did some crazy shit with pagers: https://www.japanesewithanime.com/2018/02/spelling-words-using-numbers.html

It’s difficult 2 transpose what u can do in English just 2 other languages written in the Latin alphabet for centuries. English has a remarkable and quite confusing amount of homophones that is absent from other indoeuropean languages. The apostrophe as a letter skipped marker is fairly universal. But beyond that it’s already a different ball game in other more similar languages. 2 to too, 4 for, r u - that’s very English only.

Simplified Chinese characters are a hint at what they did on the Chinese mainland to cut down on writing time. Beyond that (and I don’t speak the language so 🧂) there are single character abbreviations for countries. 美国 is America and 美 suffices as shorthand, which means beauty otherwise. Your example phrase is “R u coming 2nite?” In English we use the present progressive tense here, which doesn’t exist like that in Mandarin. It would be phrased as “Come tonight?” The question mark could be replaced with the character that functions as a question marker by itself. And I think you can do this in 3-4 characters and I think they might just beat you to it in a bilingual texting competition in terms of speed.

The mainland population may also be more adept to obfuscate their speech especially online. So similarly pronounced character combinations take over the meaning of a term the censors are actively looking for.

The Japanese like shortening stuff, mostly loanwords, to unrecognizable words. The word for part time work is アルバイト (arubaito) taken from the German for work (Arbeit). Cool kids have whittled it down to baito. A remote control has become a リモコン (rimokon) in normal parlance. Overly long Chinese character combos like 自動販売機 for a vending machine get shortened to 自販機 dropping characters that can be inferred (if you speak it).

I also want to add that text speak is heavily influenced by restrictions on text length and charges for each text. Non Latin script characters take up more than one Latin character per Chinese character for instance. It’s probably 5+ in decoding per character. So you reach 160 letters quite quickly and that’s why SMS in China was very cheap and quickly adopted a system where message threads would be sent and put back together on the recipient’s phone. In Japan they used email from the start, even in dumb phone T9 texting days. They had no Twitter-like restrictions on text length so they didn’t need to be shorter than what their thumbs could successfully fumble together.

I know for sure Korean does this, though technically their writing system is a syllabary. Symbols representing vowel and consonants are arranged into blocks that represent a syllable.

For example ㅈㅅ is short for 죄송합니다 meaning “I’m sorry”. Talk about efficient shorthand! The first consonants of each syllable block are used to makeup the shorthand, the ending 합니다 is a polite conjugation which is ignored in shorthand. You can look up “korean texting slang” for more. It’s apparently used a lot. The shorthand some might already be familiar with is ㅋㅋ which is “lol”.

I remember reading somewhere that Japanese schools girls started to write hearth shape into their symbols because it felt cute, it got out of hands at the point that teachers were obligated to banish hearth into schools

It’s already shorthand, no?