That one is priceless!
I do my best to use plain English rather than idiomatic expressions.
The language loses a bit of magic with simplicity. I’d prefer to have the idiom and a brief explanation (e.g. beware danger). The beauty of idioms is you can create new ones constantly. As long as it’s intelligible to most people, it can stick around.
No, it can’t. We create subtitles for an international public. They should be understandable for all English speakers (native or not and from all areas) and easy to translate into all other languages. We use explanations to explain terms from the source language, not for English idioms that we could have replaced with something everyone can undertand. If you want English idioms, go read some literature.
I think you do good. I try my best to do the same in French, even if we mostly use “French from France”, I try to not use too typical idiom when I have to or translate in plain French who can be internationally understood (as far as I know). After all, I might know some French from Quebec / Switzerland / Belgium and slang from Africa who is now used in France, I am far from knowing all the French from all over the world… I probably fail sometime (if I am in charge, DM me and tell me where you need more explanation…).