UX: Set silence_reason using the system locale

Previously we would use the user's locale, which can be confusing for moderators.

lib/new_post_manager.rb

@@ -157,12 +157,14 @@ class NewPostManager
 
     result = manager.enqueue(reason)
 
-    if is_fast_typer?(manager)
-      UserSilencer.silence(manager.user, Discourse.system_user, keep_posts: true, reason: I18n.t("user.new_user_typed_too_fast"))
-    elsif matches_auto_silence_regex?(manager)
-      UserSilencer.silence(manager.user, Discourse.system_user, keep_posts: true, reason: I18n.t("user.content_matches_auto_silence_regex"))
-    elsif reason == :email_spam && is_first_post?(manager)
-      UserSilencer.silence(manager.user, Discourse.system_user, keep_posts: true, reason: I18n.t("user.email_in_spam_header"))
+    I18n.with_locale(SiteSetting.default_locale) do
+      if is_fast_typer?(manager)
+        UserSilencer.silence(manager.user, Discourse.system_user, keep_posts: true, reason: I18n.t("user.new_user_typed_too_fast"))
+      elsif matches_auto_silence_regex?(manager)
+        UserSilencer.silence(manager.user, Discourse.system_user, keep_posts: true, reason: I18n.t("user.content_matches_auto_silence_regex"))
+      elsif reason == :email_spam && is_first_post?(manager)
+        UserSilencer.silence(manager.user, Discourse.system_user, keep_posts: true, reason: I18n.t("user.email_in_spam_header"))
+      end
     end
 
     result

spec/components/new_post_manager_spec.rb

@@ -182,6 +182,23 @@ describe NewPostManager do
       end
     end
 
+    context 'with a fast typer' do
+      let(:manager) { NewPostManager.new(topic.user, raw: 'this is new post content', topic_id: topic.id, first_post_checks: true) }
+      let(:user) { manager.user }
+
+      before do
+        user.update!(trust_level: 0)
+      end
+
+      it "adds the silence reason in the system locale" do
+        I18n.with_locale(:fr) do # Simulate french user
+          result = NewPostManager.default_handler(manager)
+        end
+        expect(user.silenced?).to eq(true)
+        expect(user.silence_reason).to eq(I18n.t("user.new_user_typed_too_fast", locale: :en))
+      end
+    end
+
   end
 
   context "new topic handler" do