diff --git a/i18n/bundle_test.go b/i18n/bundle_test.go
index 99706623..37f0cab1 100644
--- a/i18n/bundle_test.go
+++ b/i18n/bundle_test.go
@@ -30,6 +30,8 @@ var everythingMessage = MustNewMessage(map[string]string{
 	"few":         "few translation",
 	"many":        "many translation",
 	"other":       "other translation",
+	"leftDelim":   "<<",
+	"rightDelim":  ">>",
 })
 
 func TestConcurrentAccess(t *testing.T) {
@@ -113,7 +115,9 @@ func TestJSON(t *testing.T) {
 		"two": "two translation",
 		"few": "few translation",
 		"many": "many translation",
-		"other": "other translation"
+		"other": "other translation",
+		"leftDelim": "<<",
+		"rightDelim": ">>"
 	}
 }`), "en-US.json")
 
@@ -143,6 +147,8 @@ everything:
   few: few translation
   many: many translation
   other: other translation
+  leftDelim: "<<"
+  rightDelim: ">>"
 `), "en-US.yaml")
 
 	expectMessage(t, bundle, language.AmericanEnglish, "simple", simpleMessage)
@@ -171,6 +177,8 @@ everything:
   few: few translation
   many: many translation
   other: other translation
+  leftDelim: "<<"
+  rightDelmin: ">>"
   garbage: something
 
 description: translation
@@ -212,6 +220,8 @@ two = "two translation"
 few = "few translation"
 many = "many translation"
 other = "other translation"
+leftDelim = "<<"
+rightDelim = ">>"
 `), "en-US.toml")
 
 	expectMessage(t, bundle, language.AmericanEnglish, "simple", simpleMessage)
@@ -241,9 +251,7 @@ func TestV1Format(t *testing.T) {
 `), "en-US.json")
 
 	expectMessage(t, bundle, language.AmericanEnglish, "simple", simpleMessage)
-	e := *everythingMessage
-	e.Description = ""
-	expectMessage(t, bundle, language.AmericanEnglish, "everything", &e)
+	expectMessage(t, bundle, language.AmericanEnglish, "everything", newV1EverythingMessage())
 }
 
 func TestV1FlatFormat(t *testing.T) {
@@ -264,15 +272,21 @@ func TestV1FlatFormat(t *testing.T) {
 `), "en-US.json")
 
 	expectMessage(t, bundle, language.AmericanEnglish, "simple", simpleMessage)
-	e := *everythingMessage
-	e.Description = ""
-	expectMessage(t, bundle, language.AmericanEnglish, "everything", &e)
+	expectMessage(t, bundle, language.AmericanEnglish, "everything", newV1EverythingMessage())
 }
 
 func expectMessage(t *testing.T, bundle *Bundle, tag language.Tag, messageID string, message *Message) {
 	expected := NewMessageTemplate(message)
 	actual := bundle.messageTemplates[tag][messageID]
 	if !reflect.DeepEqual(actual, expected) {
-		t.Errorf("bundle.MessageTemplates[%q][%q] = %#v; want %#v", tag, messageID, actual, expected)
+		t.Errorf("bundle.MessageTemplates[%q][%q]\ngot  %#v\nwant %#v", tag, messageID, actual, expected)
 	}
 }
+
+func newV1EverythingMessage() *Message {
+	e := *everythingMessage
+	e.Description = ""
+	e.LeftDelim = ""
+	e.RightDelim = ""
+	return &e
+}
diff --git a/i18n/message.go b/i18n/message.go
index 30587693..7af4c9b5 100644
--- a/i18n/message.go
+++ b/i18n/message.go
@@ -192,7 +192,8 @@ var reservedKeys = map[string]struct{}{
 }
 
 func isReserved(key string, val any) bool {
-	if _, ok := reservedKeys[key]; ok {
+	lk := strings.ToLower(key)
+	if _, ok := reservedKeys[lk]; ok {
 		if key == "translation" {
 			return true
 		}
@@ -214,62 +215,44 @@ func isMessage(v interface{}) (bool, error) {
 	case nil, string:
 		return true, nil
 	case map[string]interface{}:
-		reservedKeyCount := 0
-		for key := range reservedKeys {
-			val, ok := data[key]
-			if ok && isReserved(key, val) {
-				reservedKeyCount++
+		reservedKeys := make([]string, 0, len(reservedKeys))
+		unreservedKeys := make([]string, 0, len(data))
+		for k, v := range data {
+			if isReserved(k, v) {
+				reservedKeys = append(reservedKeys, k)
+			} else {
+				unreservedKeys = append(unreservedKeys, k)
 			}
 		}
-		if reservedKeyCount == 0 {
-			return false, nil
-		}
-		if len(data) > reservedKeyCount {
-			reservedKeys := make([]string, 0, reservedKeyCount)
-			unreservedKeys := make([]string, 0, len(data)-reservedKeyCount)
-			for k, v := range data {
-				if isReserved(k, v) {
-					reservedKeys = append(reservedKeys, k)
-				} else {
-					unreservedKeys = append(unreservedKeys, k)
-				}
-			}
+		hasReservedKeys := len(reservedKeys) > 0
+		if hasReservedKeys && len(unreservedKeys) > 0 {
 			return false, &mixedKeysError{
 				reservedKeys:   reservedKeys,
 				unreservedKeys: unreservedKeys,
 			}
 		}
-		return true, nil
+		return hasReservedKeys, nil
 	case map[interface{}]interface{}:
-		reservedKeyCount := 0
-		for key := range reservedKeys {
-			val, ok := data[key]
-			if ok && isReserved(key, val) {
-				reservedKeyCount++
+		reservedKeys := make([]string, 0, len(reservedKeys))
+		unreservedKeys := make([]string, 0, len(data))
+		for key, v := range data {
+			k, ok := key.(string)
+			if !ok {
+				unreservedKeys = append(unreservedKeys, fmt.Sprintf("%+v", key))
+			} else if isReserved(k, v) {
+				reservedKeys = append(reservedKeys, k)
+			} else {
+				unreservedKeys = append(unreservedKeys, k)
 			}
 		}
-		if reservedKeyCount == 0 {
-			return false, nil
-		}
-		if len(data) > reservedKeyCount {
-			reservedKeys := make([]string, 0, reservedKeyCount)
-			unreservedKeys := make([]string, 0, len(data)-reservedKeyCount)
-			for key, v := range data {
-				k, ok := key.(string)
-				if !ok {
-					unreservedKeys = append(unreservedKeys, fmt.Sprintf("%+v", key))
-				} else if isReserved(k, v) {
-					reservedKeys = append(reservedKeys, k)
-				} else {
-					unreservedKeys = append(unreservedKeys, k)
-				}
-			}
+		hasReservedKeys := len(reservedKeys) > 0
+		if hasReservedKeys && len(unreservedKeys) > 0 {
 			return false, &mixedKeysError{
 				reservedKeys:   reservedKeys,
 				unreservedKeys: unreservedKeys,
 			}
 		}
-		return true, nil
+		return hasReservedKeys, nil
 	}
 	return false, nil
 }