You may already know that we Japanese people are fond of making a word from more than two words by abbreviating or synthesizing them.

I'm not really sure that the original phrasing is even wrong, it felt good enough to me, but "we <organization>" isn't I feel the most common phrasing. Rather, if the speaker only mentions the organization, they may be speaking as a member of that organization. Especially on a language exchange forum.

Just putting a note up here for context: A lot of my suggestions are going to be for naturalness. This was written very well and was easy to understand which makes me want to raise my standards on my suggestions.

For example, 就活, which means "job hunting", is thean abbreviated andion of the compounded word, originating from 就職活動.

"就職活動" is already a compound word, but saying 就活 is "abbreviated and compounded" makes it sound like its original form was not a "compound" itself. But also, I feel "to form a compound word" would be more natural phrasing than "compounded word".

In this case, the formerirst kanji characters of each word( 就職 and活動) are chostaken and unitcombined.

kanji: This and many loan words from Chinese and Japanese are already plural. However, even were that not the case, it should be singular. Please see these examples:

"Give one piece of candy to each student." -> do "give a piece of candy" per student
"Give two pieces of candy to each student." -> do "give two pieces of candy" per student

chosen -> taken: "Chosen" doesn't really make sense here in the English sense, but I'm not sure if there's a difference in meaning from the Japanese version.
それぞれ最初の漢字を選んで合成したものです。
Looks right to me, I just think English speakers might not use "chosen" here.

united -> combined: Unite gives me more this feeling of the combining of forces, collaborating, 協力する. Referencing the dictionary, I'm hoping the difference becomes clear:
https://www.merriam-webster.com/dictionary/unite
https://www.merriam-webster.com/dictionary/combine

There are endless examples to give in terms of this type.

More natural, I think, would be "there are countless examples of this."

As another type, 育メン, which means men who pleasingly engageenjoy participating in child-rearing, comes from the phrase育児を好む男性（メン).

You can see it in the message like this, 僕は今東京、ちな今どこ？(I am now in Tokoyo now, how about you? )

Without your translation, I would've assumed the "ちな今どこ？" meant "where are you?," but I feel like the translation kind of implies the listener is also expected to be in Tokyo.

For young people who like to take less timtry to save time while texting, it is convenient to shorten sentences or phrases ifas long as they can easily understand the meaning.

if -> as long as: This felt more natural to me. "if" feels like it implies to me they might still shorted sentences even when it cannot be easily understood whereas "as long as" feels like it much more strongly states they will shorten sentences ONLY when it can be understood, which makes more sense to me because otherwise they can't communicate effectively.

I saw ならば in the Japanese version and someone said at one point ば has that nuance of exclusivity, but I'm not sure.

I dare not to use them, but I feel uncomfortable if I don’t know their meaning.

"I dare not" is a weird phrase in modern English for not using "to," but I think "to" can't follow a "not" or other adverbs since it's a preposition.

Recently, I’ve heard a strange saying, that is もしトラ.