Apple - How can I pause the download on Mac App Store and then resume it later?

Open Launchpad and you will see your downloading app. Simply click on the app icon to pause the download, and click it again to resume.

For High Sierra 10.13 and Mojave 10.14

Open Finder, then look up for your downloading app icon under Applications, and click on the X icon to "remove" it:

Next time you start this app's download, it will resume from where it stopped.

A bit awkward but it works.