An uninstall target is not customary and would be problematic to implement correctly. And anyway, having distros package Catapult is a better way to solve (un)installation issues than some weird Makefile stuff that very few will use.

What's your need for a separate build target? There's already DESTDIR in the Makefile, which e.g. distro packages should be able to use, something like

make DESTDIR=pkg PREFIX=/usr install

Targeting catapult to be packaged by different distros seems good idea. Also uninstalling is not trivial as you said.
Having separate build target is more popular from my experience and is expected by different packaging systems - i.e. in RPM-based distro, there are separate steps build and install. Various programs use just make build and make install command in them. There are also predefined macros for that.

Another reason to have separate build target is that: as a user/packager, I would like to inspect what will be installed, like generated translation files, without performing actual installation.

Another reason is root privilege - roght now, to install Catapult I need to execute gettext command with root privileges since appropriate files are generated during install target. If there's some hypothetical vulnerability in gettext utility, it would be bad to execute it as root.

I created such new build target and can make a PR with it.

Yeah, go ahead, make a PR, we can take a look.