You only need to enter the information from box 18 IF there is an amount in box 19. You can skip over or delete any line items that do not have an amount in box 19.
If you have 2 (or more) different local tax payments in box 19, you should report BOTH/ALL as separate line items. See the image below to see how these (multiple local taxes) are reported. You can report up to 5 local tax payments on 1 W-2.
