Add details to error response for POST /api/v1/accounts in REST API (#15803)

config/locales/activerecord.en.yml

@@ -5,13 +5,28 @@ en:
       poll:
         expires_at: Deadline
         options: Choices
+      user:
+        agreement: Service agreement
+        email: E-mail address
+        locale: Locale
+        password: Password
+      user/account:
+        username: Username
+      user/invite_request:
+        text: Reason
     errors:
       models:
         account:
           attributes:
             username:
-              invalid: only letters, numbers and underscores
+              invalid: must contain only letters, numbers and underscores
+              reserved: is reserved
         status:
           attributes:
             reblog:
               taken: of status already exists
+        user:
+          attributes:
+            email:
+              blocked: uses a disallowed e-mail provider
+              unreachable: does not seem to exist

config/locales/en.yml

@@ -80,7 +80,6 @@ en:
       other: Toots
     posts_tab_heading: Toots
     posts_with_replies: Toots and replies
-    reserved_username: The username is reserved
     roles:
       admin: Admin
       bot: Bot
@@ -1410,11 +1409,8 @@ en:
       tips: Tips
       title: Welcome aboard, %{name}!
   users:
-    blocked_email_provider: This e-mail provider isn't allowed
     follow_limit_reached: You cannot follow more than %{limit} people
     generic_access_help_html: Trouble accessing your account? You may get in touch with %{email} for assistance
-    invalid_email: The e-mail address is invalid
-    invalid_email_mx: The e-mail address does not seem to exist
     invalid_otp_token: Invalid two-factor code
     invalid_sign_in_token: Invalid security code
     otp_lost_help_html: If you lost access to both, you may get in touch with %{email}