Hotkey change:

1. Change F1 from Memdisk to help
2. Add d/Ctrl+d for Memdisk
3. Add L for Language selection

So update the help txt files and menu json files at the same time.

INSTALL/grub/grub.cfg

@@ -65,6 +65,10 @@ function ventoy_vcfg_proc {
     fi
 }
 
+function ventoy_language {
+    configfile $prefix/menulang.cfg
+}
+
 function ventoy_diagnosis {
     vt_enum_video_mode    
     configfile $prefix/debug.cfg
@@ -2373,6 +2377,7 @@ set VTOY_HELP_CMD="ventoy_show_help"
 set VTOY_CHKSUM_CMD="ventoy_checksum"
 set VTOY_HELP_TXT_LANGUAGE="en_US"
 set VTOY_CHKSUM_FILE_PATH="X"
+set VTOY_LANG_CMD="ventoy_language"
 
 
 if [ "$grub_platform" = "pc" ]; then
@@ -2582,6 +2587,7 @@ export VTOY_HELP_CMD
 export VTOY_CHKSUM_CMD
 export VTOY_HELP_TXT_LANGUAGE
 export VTOY_CHKSUM_FILE_PATH
+export VTOY_LANG_CMD
 
 
 #colect all image files (iso files)