When looking for something to translate and wishing to reach the largest amount of users, one of the basic system tools is a good choice: grep, sed, tar, findutils, coreutils, and bash. After those: shared-mime-info, xdg-user-dirs, parts of libc and parts of util-linux-ng. And then maybe aspell, dialog, diffutils, e2fsprogs, gawk, kbd, make, psmisc, texinfo, wget, and xkeyboard-config. Most of the other domains are used by a relatively small number of people.