The new ebuild don't include/aply the patch apt-cacher-ng_0.6.2-1.diff from the app author. Reproducible: Always
That diff adds: 1) the usual Debian stuff, which shouldn't interest us, and it adds 2) init.d, conf.d, cron, and logrotate scripts, which we already have, and it adds 3) 14 translations. So I guess you want that last one? Simply applying the patch doesn't do anything outside the debian/ subdirectory - we would need to change CMakeLists.txt too to incorporate any of it in the build system.
I see the translation seems only also debian related so i close this bug and sorry for the mistake. Thanks