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>

config/config.exs

@@ -94,15 +94,11 @@ config :mobilizon, Mobilizon.Web.Email.Mailer,
   hostname: "localhost",
   # usually 25, 465 or 587
   port: 25,
-  # or {:system, "SMTP_USERNAME"}
   username: nil,
-  # or {:system, "SMTP_PASSWORD"}
   password: nil,
   # can be `:always` or `:never`
   tls: :if_available,
-  # or {":system", ALLOWED_TLS_VERSIONS"} w/ comma seprated values (e.g. "tlsv1.1,tlsv1.2")
   allowed_tls_versions: [:tlsv1, :"tlsv1.1", :"tlsv1.2"],
-  # can be `true`
   retries: 1,
   # can be `true`
   no_mx_lookups: false