Language change implementation revamped. Didn't work as intended with Arduino IDE.

Marlin/dogm_lcd_implementation.h

 
 /* Russian language not supported yet, needs custom font
 
-#if LANGUAGE_CHOICE == ru
+#ifdef LANGUAGE_RU
 #include "LiquidCrystalRus.h"
 #define LCD_CLASS LiquidCrystalRus
 #else

Marlin/language.h

 #ifndef LANGUAGE_H
 #define LANGUAGE_H
 
+#define LANGUAGE_CONCAT(M)       #M
+#define GENERATE_LANGUAGE_INCLUDE(M)  LANGUAGE_CONCAT(language_##M.h)
+
+
 // NOTE: IF YOU CHANGE LANGUAGE FILES OR MERGE A FILE WITH CHANGES
 //
-//   ==> ALWAYS TRY TO COMPILE MARLIN WITH/WITHOUT "ULTIPANEL" / "ULTRALCD" / "SDSUPPORT" #define IN "Configuration.h" 
-//   ==> ALSO TRY ALL AVAILABLE "LANGUAGE_CHOICE" OPTIONS
+//   ==> ALWAYS TRY TO COMPILE MARLIN WITH/WITHOUT "ULTIPANEL" / "ULTRALCD" / "SDSUPPORT" #define IN "Configuration.h"
+//   ==> ALSO TRY ALL AVAILABLE LANGUAGE OPTIONS
 
 // Languages
 // en English
 // ca Catalan
 // eu Basque-Euskera
 
-#ifndef LANGUAGE_CHOICE
-	#define LANGUAGE_CHOICE en  // Pick your language from the list above
-#endif
-
-#if LANGUAGE_CHOICE >= 1
-  #error "Languages now uses ISO language codes instead of numbers."
+#ifndef LANGUAGE_INCLUDE
+  // pick your language from the list above
+  #define LANGUAGE_INCLUDE GENERATE_LANGUAGE_INCLUDE(en)
 #endif
 
 #define PROTOCOL_VERSION "1.0"
 
 #if MB(ULTIMAKER)|| MB(ULTIMAKER_OLD)|| MB(ULTIMAIN_2)
-	#define MACHINE_NAME "Ultimaker"
-	#define FIRMWARE_URL "http://firmware.ultimaker.com"
+  #define MACHINE_NAME "Ultimaker"
+  #define FIRMWARE_URL "http://firmware.ultimaker.com"
 #elif MB(RUMBA)
-	#define MACHINE_NAME "Rumba"
-	#define FIRMWARE_URL "https://github.com/ErikZalm/Marlin/"
+  #define MACHINE_NAME "Rumba"
+  #define FIRMWARE_URL "https://github.com/ErikZalm/Marlin/"
 #elif MB(3DRAG)
-	#define MACHINE_NAME "3Drag"
-	#define FIRMWARE_URL "http://3dprint.elettronicain.it/"
+  #define MACHINE_NAME "3Drag"
+  #define FIRMWARE_URL "http://3dprint.elettronicain.it/"
 #elif MB(5DPRINT)
-	#define MACHINE_NAME "Makibox"
-	#define FIRMWARE_URL "https://github.com/ErikZalm/Marlin/"
+  #define MACHINE_NAME "Makibox"
+  #define FIRMWARE_URL "https://github.com/ErikZalm/Marlin/"
 #else
-	#ifdef CUSTOM_MENDEL_NAME
-		#define MACHINE_NAME CUSTOM_MENDEL_NAME
-	#else
-		#define MACHINE_NAME "Mendel"
-	#endif
+  #ifdef CUSTOM_MENDEL_NAME
+    #define MACHINE_NAME CUSTOM_MENDEL_NAME
+  #else
+    #define MACHINE_NAME "Mendel"
+  #endif
 
 // Default firmware set to Mendel
-	#define FIRMWARE_URL "https://github.com/ErikZalm/Marlin/"
+  #define FIRMWARE_URL "https://github.com/ErikZalm/Marlin/"
 #endif
 
 
 #define MSG_SD_PRINTING_BYTE                "SD printing byte "
 #define MSG_SD_NOT_PRINTING                 "Not SD printing"
 #define MSG_SD_ERR_WRITE_TO_FILE            "error writing to file"
-#define MSG_SD_CANT_ENTER_SUBDIR 			"Cannot enter subdir: "
+#define MSG_SD_CANT_ENTER_SUBDIR      "Cannot enter subdir: "
 
 #define MSG_STEPPER_TOO_HIGH                "Steprate too high: "
 #define MSG_ENDSTOPS_HIT                    "endstops hit: "
 #define MSG_BABYSTEPPING_X                  "Babystepping X"
 #define MSG_BABYSTEPPING_Y                  "Babystepping Y"
 #define MSG_BABYSTEPPING_Z                  "Babystepping Z"
-#define MSG_SERIAL_ERROR_MENU_STRUCTURE		"Error in menu structure"
+#define MSG_SERIAL_ERROR_MENU_STRUCTURE   "Error in menu structure"
 
 // LCD Menu Messages
 
-#if   LANGUAGE_CHOICE == en // English
-  #include "language_en.h"
-#elif LANGUAGE_CHOICE == pl // Polish
-  #include "language_pl.h"
-#elif LANGUAGE_CHOICE == fr // French
-  #include "language_fr.h"
-#elif LANGUAGE_CHOICE == de // German
-  #include "language_de.h"
-#elif LANGUAGE_CHOICE == es // Spanish
-  #include "language_es.h"
-#elif LANGUAGE_CHOICE == ru // Russian
-  #include "language_ru.h"
-#elif LANGUAGE_CHOICE == it // Italian
-  #include "language_it.h"
-#elif LANGUAGE_CHOICE == pt // Portuguese
-  #include "language_pt.h"
-#elif LANGUAGE_CHOICE == fi // Finnish
-  #include "language_fi.h"
-#elif LANGUAGE_CHOICE == an // Aragonese
-  #include "language_an.h"
-#elif LANGUAGE_CHOICE == nl // Dutch
-  #include "language_nl.h"
-#elif LANGUAGE_CHOICE == ca // Catalan
-  #include "language_ca.h"
-#elif LANGUAGE_CHOICE == eu // Basque-Euskera
-  #include "language_eu.h"
-#endif
+#include LANGUAGE_INCLUDE
 
 #endif //__LANGUAGE_H

Marlin/language_ru.h

 #ifndef LANGUAGE_RU_H
 #define LANGUAGE_RU_H
 
+#define LANGUAGE_RU
+
 #define WELCOME_MSG                         MACHINE_NAME "Готов."
 #define MSG_SD_INSERTED                     "Карта вставлена"
 #define MSG_SD_REMOVED                      "Карта извлечена"

Marlin/ultralcd_implementation_hitachi_HD44780.h

 
 #else
   // Standard directly connected LCD implementations
-  #if LANGUAGE_CHOICE == ru
+  #ifdef LANGUAGE_RU
     #include "LiquidCrystalRus.h"
     #define LCD_CLASS LiquidCrystalRus
   #else