LocalisationUpdate is bundled in the standard MediaWiki core tarball, but:

• isn't selected for installation by default (no extension is),
• doesn't set up the required crontabs even when selected.

Automatic updates of i18n are desirable for a number of reasons, the most important ones being:

1. most MediaWiki installations out there are only updated once every several years, but often use incomplete localisations which in the meanwhile have been completed;
2. system messages may contain important updates for wiki users and sysadmins, like T85456.

An effort to this purpose was started in January 2014, but abandoned in September 2014. https://gerrit.wikimedia.org/r/#/c/105514/3