@org.springframework.boot.autoconfigure.AutoConfiguration(beforeName = "org.grails.plugins.i18n.I18nAutoConfiguration")
@org.springframework.boot.autoconfigure.condition.ConditionalOnWebApplication(type = ConditionalOnWebApplication.Type.SERVLET)
@org.springframework.context.annotation.Import(GrailsLocaleResolverAutoConfiguration.RemoveWebMvcSupportLocaleResolverRegistrar.class)
public class GrailsLocaleResolverAutoConfiguration
extends java.lang.Object

When an application declares @EnableWebMvc, Spring's WebMvcConfigurationSupport contributes its own localeResolver bean (an AcceptHeaderLocaleResolver). That bean exists before I18nGrailsPlugin's generated I18nAutoConfiguration is evaluated, so its @ConditionalOnMissingBean(name = "localeResolver") backs off and Grails' configured resolver (a SessionLocaleResolver by default) never registers — silently disabling ?lang= switching. This was not the case before WebMvcConfigurationSupport gained a localeResolver bean: Grails' resolver used to take precedence, matching Grails 7 behavior.

This removes the WebMvcConfigurationSupport-contributed localeResolver so that I18nGrailsPlugin's generated auto-configuration registers the Grails-configured resolver instead. A localeResolver contributed by the application itself (for example via resources.groovy or a user @Configuration) is left untouched, so an explicit application resolver still wins. Ordered before that generated auto-configuration (by name, since it does not exist as a compilable class for this class to reference directly) so the removal happens before its condition is evaluated.