[EN] Various fixes for UI files

[Faalagorn]

Originally started as a follow-up to my previous changes from #267 that didn't get merged, but I probably spent too much time fixing all other minor issues I found, starting from wording, casing, empty spaces and tabs as well as comments.

Turned out to be quite a big change and it might conflict with my other PRs such as #462 so I'm holding on further changes until they are solved; let me know if you want me to merge my edits together or split them into smaller ones!

Also let me know if something is wrong or controversial, as that's quite a few changes to chew through, might be a little too much at once, but I can address them one by one.