Please cherry-pick:

Please cherry-pick:
- changed List to Map to have locale name (e.g. de_DE) as key and the locale
  itself as value stored in a map for a quick lookup
- this map is also being used to handle browser's language-only locales, like
  "de" and not "de_AT" or other equivalents
- there is now a submit button for JS-less users to change locale

Signed-off-by: Roland Häder <roland@mxchange.org>