Fix ExtUI compile errors (#17544)

Fixes #16628

Marlin/src/core/multi_language.h

@@ -76,7 +76,7 @@ typedef const char Language_Str[];
 #endif
 #define GET_TEXT_F(MSG) (const __FlashStringHelper*)GET_TEXT(MSG)
 
-#define MSG_CONCAT(A,B) pgm_p_pair_t(GET_TEXT(A),GET_TEXT(B))
+#define GET_LANGUAGE_NAME(INDEX) GET_LANG(LCD_LANGUAGE_##INDEX)::LANGUAGE
 
 #define MSG_1_LINE(A)     A "\0"   "\0"
 #define MSG_2_LINE(A,B)   A "\0" B "\0"