Complete the contributed translations against the current English source and
register the locales in the language picker.
Fills the 51 keys the contributions predated, including the whole
downloads.backgroundWarning block that every locale must translate, and
restores the ${count} placeholder the sync-rule confirmation had dropped in all
three files.
Also corrects contributed strings: Azerbaijani "Imkan (Kopyalama)"
(possibility/copying) for resolution and several Turkish spellings, and Kazakh
Latin-script leaks ("Keyinirek", "Subtitr") plus Uzbek loanwords ("бош", "бир",
"муаммо") that do not read as Kazakh.
Consolidates #1689, #1690, and #1691.
Co-authored-by: Omc725 <98108290+Omc725@users.noreply.github.com>
