Allow selecting default posting language instead of auto-detect (#7828)

* Allow selecting default posting language instead of auto-detect

* Enable default language setting in credentials API

* Fix form saving

app/controllers/api/v1/accounts/credentials_controller.rb

@@ -32,6 +32,7 @@ class Api::V1::Accounts::CredentialsController < Api::BaseController
     {
       'setting_default_privacy' => source_params.fetch(:privacy, @account.user.setting_default_privacy),
       'setting_default_sensitive' => source_params.fetch(:sensitive, @account.user.setting_default_sensitive),
+      'setting_default_language' => source_params.fetch(:language, @account.user.setting_default_language),
     }
   end
 end