Fix language change

- Load the language files correctly when language is changed
- Save user language in localstorage so that we can have it even if disconnected (but still load it from user settings eventually since
user might be on a different device)
- Load all locales from Cldr with Gettext
- Fix pt-PT -> pt-BR
- Clean some obsolete config.exs comments

Later changes will allow to set the language without an account
https://framagit.org/framasoft/mobilizon/-/issues/375

Signed-off-by: Thomas Citharel <tcit@tcit.fr>

js/src/i18n/langs.json

@@ -15,7 +15,7 @@
   "oc": "Occitan",
   "pl": "Polski",
   "pt": "Português",
-  "pt_PT": "Português (Portugal)",
+  "pt_BR": "Português brasileiro",
   "ru": "Русский",
   "sv": "Svenska"
 }