In distributions like Ubuntu, /usr is where packages are supposed to install stuff and /usr/local is where the system administrator can install stuff outside the packaging system. From the Filesystem Hierarchy Standard:
The /usr/local hierarchy is for use by the system administrator when
installing software locally. It needs to be safe from being
overwritten when the system software is updated. It may be used for
programs and data that are shareable amongst a group of hosts, but not
found in /usr.
Locally installed software must be placed within /usr/local rather
than /usr unless it is being installed to replace or upgrade
software in /usr.
/usr/locale seems to be a mistake in packaging. It contains translations of text used by some Unity lenses, but those are supposed to go in /usr/share. For example, here's the directory structure of /usr/locale:
~ find /usr/locale
/usr/locale
/usr/locale/da
/usr/locale/da/LC_MESSAGES
/usr/locale/da/LC_MESSAGES/unity-lens-files.mo
/usr/locale/da/LC_MESSAGES/unity-lens-applications.mo
And in /usr/share/locale, one will find hundreds of such files:
$ find /usr/share/locale | head
/usr/share/locale
/usr/share/locale/tig
/usr/share/locale/tig/LC_MESSAGES
/usr/share/locale/tig/LC_MESSAGES/iso_639_3.mo
/usr/share/locale/tig/LC_MESSAGES/iso_3166.mo
/usr/share/locale/tig/LC_MESSAGES/iso_639.mo
/usr/share/locale/hsb
/usr/share/locale/hsb/kf5_entry.desktop
/usr/share/locale/hsb/LC_MESSAGES
/usr/share/locale/hsb/LC_MESSAGES/kjobwidgets5_qt.qm
Packages are not supposed to create more directories in the top level of /usr. This seems to be a harmless bug. You may report it if you feel like it.