As part of T359918: Lua interface for convenient access to translations in a message bundle we implemented a simple cache expiry mechanism that invalidates the cache of all templates that use the message bundle whenever the message bundle is updated or a translation is made.

This is wasteful because irrespective of what language translation is made, all the templates using the message bundle are purged.

A few things to keep in mind:

• There’s no easy way to determine the affected pages when a message bundle is updated. Especially as the requested message bundle language can be user-controlled, so checking the page language isn’t enough.
• We use the language fallback chain (unless explicitly disabled by the module calling us), so if a translation doesn’t exist, all non-existing translations in the chain (in case one of them is created) and the first existing message in the chain (in case it’s edited – or deleted) need to be tracked.
• Considering tracking dependencies on a key level. There is a possibility that multiple templates might decide to use a single large message bundle.
• For Commons, depending on the approach we take here, we may have to put dependency tracking behind a feature flag or have our own table that tracks the dependencies.
• In an ideal scenario one bundle will serve one module, causing most of the individual messages to be used on most pages using the module/bundle.