What principles should be followed in the abbreviation of English words? In the past, it was said to take the first to the last letter of a word (for example, it seems to take the first, second and penultimate letter)?

The abbreviation of English words is to write that people can understand it or not, at least when they read it, they can know what it is. So it's better not to save vowels according to accent, and not to pronounce consonants according to pronunciation. For example, people on my side often write DAT, and then love is luv, u is here

What are the rules for abbreviating English words?
(e.g. which letters to choose)
I mean the abbreviation of a word, not a phrase.

Generally speaking, it's OK to take the initials, countries, organizations, etc. (such as WTO: World Trade Organization; U.S.A: United States of America)
Take the first three letters (such as April, abbreviated as Apr.) for the month and date, and take the first three letters for the common abbreviations
The rest depends on the specific situation and needs special memory

The rules of English word abbreviation
Look at the messages in "Zhiming and Chunjiao" and use some English abbreviations, such as "HV = have", "c u later = see you later" and so on. It's very convenient and handsome. Who knows how these abbreviations come from? What's the rule to follow?

Generally speaking, it is pronunciation. If the pronunciation is the same as a certain letter, it is directly abbreviated
where r u?= where are you?
The rest is usually the first few letters: popu = population

English translation
it has been closely associated with the UNIX system where it was developed,since both the system and most of the programs that run on it are written in C
The others are simple. The key is where it was developed

It's not a target adverbial. It's just a modification of the UNIX system that has been developed. It should be a clause similar to an attributive. It can be replaced by in which, and then you will know that it has nothing to do with the target adverbial

What principles should be followed in the abbreviation of English words? In the past, it was said to take the first to the last letter of a word (for example, it seems to take the first, second and penultimate letter)?