implement SI units for distance / speed measurement, closes #2496

src/localisation/string_ids.h

@@ -1407,6 +1407,11 @@ enum {
 	STR_SAVE_EVERY_HOUR = 2705,
 	STR_SAVE_NEVER = 2706,
 
+	STR_UNIT_SUFFIX_FEET = 2732,
+	STR_UNIT_SUFFIX_METRES = 2733,
+	STR_UNIT_SUFFIX_MILES_PER_HOUR = 2734,
+	STR_UNIT_SUFFIX_KILOMETRES_PER_HOUR = 2735,
+
 	STR_DATE_FORMAT_DMY = 2737,
 
 	STR_ROLLERCOASTER_TYCOON_1_DROPDOWN = 2740,
@@ -2182,6 +2187,9 @@ enum {
 
 	STR_TRAP_MOUSE = 5582,
 
+	STR_UNIT_SUFFIX_METRES_PER_SECOND = 5583,
+	STR_SI = 5584,
+
 	// Have to include resource strings (from scenarios and objects) for the time being now that language is partially working
 	STR_COUNT = 32768
 };