Also the message parameters (if any) need be available separately.

I stumbled across this task while investigating T317793: [EPIC] Deprecate EventLogging::schemaValidate().

EventLogging::schemaValidate() allows callers to validate data against pre-draft-03 (maybe) JSON Schema schemas. This is not ideal. EventLogging should only be concerned logging analytics events. Those callers should be updated to use some standard JSON Schema validation library. I figured that since MediaWiki Core uses justinrainbow/json-schema, then that's the best option but, as you've encountered here, there are situations where validation errors are shown to users so they'll need to be localised.

Fixing the above is very much a 10% project for me but I'd be more than happy to help out with this effort in that time.

So far I've noted that:

• justinrainbow/json-schema@5.2.13 can't support this cleanly
  • JsonSchema\Validator#getErrors() returns a list of error descriptors
  • The error descriptors have message, constraint, and more properties
  • message is the complete error message in English
  • In principle, constraint and more should be be enough to reconstruct message
  • In practice, the above is not true for the following values of constraint:
    • dependencies
    • additionalItems
    • format
    • additionalProp
    • requires
    • type
• justinrainbow/json-schema@dev can support this
  • With https://github.com/justinrainbow/json-schema/pull/364 landed (see also https://github.com/justinrainbow/json-schema/issues/363 from @Harej), the value of the constraint key is enough to reconstruct the value of the message key 🎉

OTOH, according to T351878: Consider downgrading opis/json-schema to version 1.1, CC 1.0 is using opis/json-schema 2.x. That task notes that the WikiLambda team decided to use opis/json-schema 1.x. This is also confirmed in T290274#7432359, which is relevant to this task.

The WikiLambda team have done a bunch of work to map opis/json-schema 1.x validation errors to their domain: https://gerrit.wikimedia.org/r/plugins/gitiles/mediawiki/extensions/WikiLambda/+/ce13fca4ff34e67a56b86498bdef23db075287f7/includes/ZErrorFactory.php#71

Sadly, due to the library version locks that we find for both Opis 2.x and justinrainbow/json-schema@dev we're considering this task a post MVP. At that point we will consider WikiLambda's approach for i18n with Opis 1.X. Thank you so much for the insightful information @phuedx.