fix(review-filter): apply language for review filter stage

internal/config/template/template.go

@@ -157,14 +157,17 @@ func resolveLang(lang string) string {
 }
 
 // ApplyLanguage injects a language directive into all system-role messages
-// across MAIN_TASK, PLAN_TASK (if set), and MEMORY_COMPRESSION_TASK.
+// across MAIN_TASK, PLAN_TASK (if set), MEMORY_COMPRESSION_TASK, and REVIEW_FILTER_TASK (if set).
 func (t *Template) ApplyLanguage(lang string) {
 	instruction := "\n\nAlways respond in " + resolveLang(lang) + "."
 	applyLanguage(&t.MainTask, instruction)
 	if t.PlanTask != nil {
 		applyLanguage(t.PlanTask, instruction)
 	}
 	applyLanguage(&t.MemoryCompressionTask, instruction)
+	if t.ReviewFilterTask != nil {
+		applyLanguage(t.ReviewFilterTask, instruction)
+	}
 }
 
 // ApplyLanguage injects a language directive into all system-role messages

internal/config/template/template_test.go

@@ -146,6 +146,12 @@ func TestApplyLanguage(t *testing.T) {
 	if !strings.HasSuffix(tpl.MemoryCompressionTask.Messages[0].Content, suffix) {
 		t.Errorf("MemoryCompressionTask system message does not end with %q", suffix)
 	}
+	if tpl.ReviewFilterTask == nil {
+		t.Fatal("ReviewFilterTask should be present in default template")
+	}
+	if !strings.HasSuffix(tpl.ReviewFilterTask.Messages[0].Content, suffix) {
+		t.Errorf("ReviewFilterTask system message does not end with %q", suffix)
+	}
 }
 
 func TestApplyLanguage_DefaultEnglish(t *testing.T) {
@@ -319,6 +325,18 @@ func TestApplyLanguage_SkipsNonSystemMessages(t *testing.T) {
 	}
 }
 
+func TestApplyLanguage_NilReviewFilterTask(t *testing.T) {
+	// ApplyLanguage should not panic when ReviewFilterTask is nil.
+	tpl := &Template{
+		MainTask:              LlmConversation{Messages: []ChatMessage{{Role: "system", Content: "sys"}}},
+		MemoryCompressionTask: LlmConversation{Messages: []ChatMessage{{Role: "system", Content: "compress"}}},
+	}
+	tpl.ApplyLanguage("German")
+	if !strings.Contains(tpl.MainTask.Messages[0].Content, "German") {
+		t.Error("MainTask should contain language directive")
+	}
+}
+
 func TestResolveLang(t *testing.T) {
 	if got := resolveLang(""); got != "English" {
 		t.Errorf("resolveLang(\"\") = %q, want \"English\"", got)