Language selection auto-save option (#20915)

Marlin/Configuration_adv.h

   //#define LCD_LANGUAGE_3 de
   //#define LCD_LANGUAGE_4 es
   //#define LCD_LANGUAGE_5 it
+  #ifdef LCD_LANGUAGE_2
+    //#define LCD_LANGUAGE_AUTO_SAVE // Automatically save language to EEPROM on change
+  #endif
 #endif
 
 //

Marlin/src/lcd/menu/menu_language.cpp

 
 static void set_lcd_language(const uint8_t inlang) {
   ui.set_language(inlang);
-  (void)settings.save();
+  TERN_(LCD_LANGUAGE_AUTO_SAVE, (void)settings.save());
 }
 
 void menu_language() {