Fix typo thanks to @wavexx

lang/lang_en_de.txt

@@ -1360,7 +1360,7 @@
 
 #MSG_MMU_MODE c=8
 "MMU Mode"
-"/x00"
+"\x00"
 
 #MSG_MODE_CHANGE_IN_PROGRESS c=20 r=3
 "Mode change in progress ..."