Translations: Fix some typos involving printf-like placeholders.
Update translations from Transifex:

 - Czech
 - Galician
 - Swedish
Language menu: Ensure "Language" always appears in English in menu entry.

If "Language" doesn't appear in the translated string, "(Language)" will be appended automatically.
Language menu: Use submenus to group language names starting with the same character.
Update translations from Transifex:

 - Greek.