To English native speakers...do these sentences sound perfect to you?

Question

Can you find any mistakes and misfits?


45 years after joining the AIEA, Russia and other member countries have made a bitter sweet journey together with the organization. Solidarity has been established and manifested not only in oil policies but also in a mutually supportive cooperation in international forums and in economic and cultural cooperations. Their varied strengths and weaknesses have made the cooperation become more important since they are complementing each other.

Answer 1

45 years after joining the AIEA, Russia and other member countries have made

Don't use present perfect with a specific time. You can say (if that's what you mean) "in the 45 years since they joined the AIEA" with "have made".


a bitter sweet journey together with the organization.

I would say "taken" a journey, not "made". Do you mean "within" the organization? It's odd for the members to do something with the organization.


Solidarity has been established and manifested not only in oil policies but also in a mutually supportive cooperation in international forums and in economic and cultural cooperations.

Parallellism would suggest that this means "Solidarity has been established in oil prices and manifested in oil prices". I don't know what that means. Not too clear what "solidarity" means here at all, really.
You need the same kind of thing after "not only" as after "but also". If that's what you have, the solidarity must be established in "a mutually supportive cooperation...in economic and cultural cooperations", ie, in a "cooperation in cooperations".
"Cooperation" is very rarely a countable noun; it shouldn't be pluralized here.


Their varied strengths and weaknesses have made the cooperation become more important since they are complementing each other.

Who or what are they/their? Grammar would suggest "they" are cooperations, but that makes little or no sense.
"Made" includes the meaning of "become" so "become" is redundant here.

Answer 2

A note about numbers (a lot of native speakers make mistakes here): There are 2 rules to remember-
1. When the first word of a sentence is a number, it must be spelled out- always. (Forty-five instead of 45)
2. When a number is NOT the first word in a sentence: numbers 1-10 should be written as numerals (numbers), but numbers that are more than 10 (everything from 11 and on) must be spelled out.

Someone else has already dissected the rest of your sentences so I'll leave that alone.

I'm assuming that English isn't your native language; if that's the case, I think you did a very nice job working with a foreign language.

(A quick note that's not really all that important: rather than English native speakers, say native English speakers. 'Native' and 'English' both describe the 'speakers' and sometimes, as in this case, the order of the descriptive words (adjectives) changes the meaning of the phrase a bit)

Answer 3

I think it sounds good, I would just change "...since they are complimenting each other" to "since they compliment each other". "Complimenting each other" is the gerund form of the verb, and isn't used that often unless you are in the process of witnessing it being happend or it is in the middle of happening. That's just my opinion, though.

Also, how are they complimenting each other? Economically? Environmentally? Militarily?

Other than those two things, I think it is very well written!