Fix #11054: Prevent translation of currency codes.

Most languages stick with the 3-letter latin currency codes in the name
string, however some translations are... clever... and use the currency
symbol instead. Whilst this may look nice, it can cause issues with fonts
as some scripts have a specific limited set of fonts which do not include
these symbols.

Instead, hard code the currency code list and add it when drawing the
currency name.

src/newgrf.cpp

@@ -2710,6 +2710,7 @@ static ChangeInfoResult GlobalVarChangeInfo(uint gvid, int numinfo, int prop, By
 
 				if ((newone != STR_UNDEFINED) && (curidx < CURRENCY_END)) {
 					_currency_specs[curidx].name = newone;
+					_currency_specs[curidx].code.clear();
 				}
 				break;
 			}