RE: What if we all would Speak One Native Language?

As far as this text goes, your English reads fine. Usually, I read German, because that's the language I need improvement in, after so many years in Germany still. Your English writing is a damn sight better than my German! So don't worry, you will never fully grasp a foreign language, and neither will anyone else. This privilege is reserved to young children and perhaps people with a talent for languages.

I can only recommend to you to read as much as you can in English. Literature, popular and classic, as many books and magazine articles as your time allows. It will also help to watch as many English language films / series / documentaries as possible, especially if you want to speak and not just write the language.

The big problem is, English is a very idiomatic language, and idioms vary depending on the world region the speaker is from: U.S.A., Australia, U.K., Carribean, etc., etc.... You can't translate idioms properly, you can only try to grasp when to use which one. That's why you feel you can't express yourself fully: because you don't know the proper idiom in English, or a German idiom doesn't translate in a meaningful way; and dictionaries / Deepl are very little help here.

Example:

"When it rains it pours!" (American)
Deepl: "Wenn es regnet, schuettet es!" (ziemlicher Unsinn)
Richtig: "Ein Unglueck kommt selten allein!"
Alternative: "Misery loves company!"

You have to know both idioms in both languages to get a good translation. Now add your local German dialect to that mix. Here in Saarland they say very drastically "Der Teufel schei..t immer auf einen Haufen!" which is a much stronger sentiment than the High German expression. Being a military brat, I would express that perhaps as "a regular clusterf.ck" - good luck running that trough Deepl...

I did a quick google on idioms for you, and this page is very helpful:
https://7esl.com/american-idioms/

Some comes down to sheer talent, though. My hubby, native German, speaks better English than I, after only 15 years in the U.S. - and not just American English, but also British. He soaks up stuff like a sponge and retains it. (He's also a reader.) Often I ask him "How do you spell that?" and he routinely has to translate British English (e.g. Cockney) into American for me, when we watch TV shows from the U.K.. I don't understand a word of what these Limeys are talking about :)

His grasp of language is a talent. I don't have it, so I'm not gonna worry about it. Neither should you. All you can do, is all you can do, and all you can do is enough.

Cheers - Caroline