Complete the contributed translation against the current English source and
register Turkish in the language picker.
Fills the 51 keys the contribution predated, including the whole
downloads.backgroundWarning block that every locale must translate, and
corrects a few contributed strings: "Sesi Kıs" (volume down) for mute,
"Disket" (floppy) for disc, "bitiş hızı" (finishing speed) for bitrate, and a
"Kısayol Ayaıla" typo.
Consolidates #1683 and #1688, which contributed byte-identical files.
Co-authored-by: Omc725 <98108290+Omc725@users.noreply.github.com>
