Berstigma

Does this mean I have two versions installed or it's just installation history?

No, "Superseded" is an older version of the same package. I tried to remove it, and it automatically removed both "Superseded" and...

I've noticed that some packages are present more than once, with one package having state "Installed" and the others having state...

What I've observed is that even if you delete a language pack, it's just hidden from the Language tab, but it's actually still installed...