We're configuring a ParameterMessageInterpolator as a fallback in case getting the default one throws an exception. Most Servlet container bring their own EL implementation, but we also provide a spring-boot-starter-validation that brings a default EL implementation for users.

This issue is about avoiding mandatory WARN logs during application startup for a deliberate choice.

Now I'm a bit confused - are you suggesting that using a ParameterMessageInterpolator when no EL implementation is available is not a valid use case?
If an application is using EL-dependent annotations with an ParameterMessageInterpolator, I'd argue that it's probably user error, but the outcome of that (processing uninterpolated messages or failing hard?) is probably hibernate's choice.