enable be locale (#22022)

It already has 80+% completion, which is enough for everyday use.
Test instance runs on https://meowstodon.net/

config/application.rb

@@ -71,6 +71,7 @@ module Mastodon
       :af,
       :ar,
       :ast,
+      :be,
       :bg,
       :bn,
       :br,