Message source that you can use to get all message keys (including plugins)

ExposedKeysMessageSource.groovy

// src/groovy folder
package com.wordpress.sergiosmind.i18n

import org.codehaus.groovy.grails.context.support.PluginAwareResourceBundleMessageSource

class ExposedKeysMessageSource extends PluginAwareResourceBundleMessageSource {
  
	Set getAllKeys(Locale locale) {
		Set applicationKeys = getMergedProperties(locale).getProperties().keySet()
		Set pluginsKeys = getMergedPluginProperties(locale).getProperties().keySet()
		
		Set resultSet = [] as Set
		resultSet.addAll(applicationKeys)
		resultSet.addAll(pluginsKeys)
		
		return resultSet
	}
}