Document MessageSource auto-configuration #15228
Description
On stack overflow I answered several question regarding messages not getting resolved. This was mainly due to a missing messages.properties or rather (<basename>.properties) which triggers the auto configuration for the MessageSource.
The documentation doesn't state that anywhere and you would have to look at (and understand) the ResourceBundleCondition in the MessageSourceAutoConfiguration.
I think it would be worthwhile to add a small section on configuring I18N with Spring Boot to the reference guide.