In media tags, what is a charset? What is the difference between English & Unicode? How can I find out on a song which charset it's using?

I was trying to use an ID tag fixer & it was telling me to make sure I'm using the right one.

Also, I manually went in via USB to fix some of the tags. It let me fix most, but some wouldn't let me change the tag. I either got an error & in some cases, nothing happened, it just wouldn't save the changes.

Please help!

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