Language Packs: Many many fixes such as:
- Add a "Update Translations" stand-alone button to the updates page
- Shift Language feedback to before update process completion action links & limit the verbosity of output (name + success/errors)
- Simplify/combine the language update descriptive string to only include a plugin/theme name
- Properly handle cache clearing after language updates to prevent langs being repeditively updated
- Display a "All items up to date" string when there's nothing to do
- Reduce the 'Connection Information' from a <h2> to a <h3> to remove duplicate h2's and screen icons from update screens
- Fix the Direct filesystem method not being used for Language updates because WP_LANG_DIR doesn't exist (check it's parent for writable instead)
See #18200, #22704


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