Right now translation builds are serialized by the build-{po,ts}files.cmake scripts. This makes no use of the job count passed to make and as a result makes builds that include a whole lot of translations (e.g. plasma-workspace) take much longer than necessary as neither CPU nor disk resources are properly utilized. Translations builds should parallelize to make full use of the available job count.
https://phabricator.kde.org/D10776