I believe the 5% rule applies to all academic journals globally because there's a 100% possibility you'll have to cite or copy a few lines from someone else's work
Nothing wrong with that, as long as you add it to your long list of references.Quote
without even realizing it
That's not possible. You'll know when you copy something.Quote
No academic publication or paper can pass a plagiarism test with a score of 0%.
If you're talking about an automated plagiarism checker, then sure, they'll always find something. But that doesn't mean it's really plagiarism.As a test, I ran everything I typed above through the first plagiarism checker I found (Grammarly). It shows: "Significant plagiarism found", which is BS.
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Academic work is continued work + added value.
And references 
You can't continue or add value without making it verifiable.