add new locale endpoint that returns the messages

services/src/main/java/org/keycloak/services/resources/KeycloakApplication.java

@@ -109,6 +109,7 @@ public class KeycloakApplication extends Application {
 
             singletons.add(new ObjectMapperResolver());
             classes.add(WelcomeResource.class);
+            classes.add(LocaleResource.class);
 
             platform.onStartup(this::startup);
             platform.onShutdown(this::shutdown);

services/src/main/java/org/keycloak/services/resources/LocaleResource.java

@@ -0,0 +1,93 @@
+package org.keycloak.services.resources;
+
+import jakarta.ws.rs.GET;
+import jakarta.ws.rs.Path;
+import jakarta.ws.rs.PathParam;
+import jakarta.ws.rs.Produces;
+import jakarta.ws.rs.QueryParam;
+import jakarta.ws.rs.core.Context;
+import jakarta.ws.rs.core.MediaType;
+import org.keycloak.models.KeycloakSession;
+import org.keycloak.models.RealmModel;
+import org.keycloak.services.managers.RealmManager;
+import org.keycloak.services.util.LocaleUtil;
+import org.keycloak.theme.Theme;
+
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Locale;
+import java.util.Map;
+import java.util.Properties;
+import java.util.Set;
+
+import static java.util.stream.Collectors.*;
+
+@Path("/localisation")
+@Produces(MediaType.APPLICATION_JSON)
+public class LocaleResource {
+
+    @Context
+    protected KeycloakSession session;
+
+    @GET
+    @Path("{realm}/{theme}/{locale}")
+
+    public List<KeySource> getLocalizationTexts(@PathParam("realm") String realmName, @PathParam("theme") String theme,
+                                                @PathParam("locale") String localeString, @QueryParam("source") boolean showSource) throws IOException {
+        RealmManager realmManager = new RealmManager(session);
+        RealmModel realm = realmManager.getRealmByName(realmName);
+        session.getContext().setRealm(realm);
+
+        Theme theTheme = session.theme().getTheme(Theme.Type.valueOf(theme.toUpperCase()));
+        final Locale locale = Locale.forLanguageTag(localeString);
+        if (showSource) {
+            Properties messagesByLocale = theTheme.getMessages("messages", locale);
+            Set<KeySource> result = messagesByLocale.entrySet().stream().map(e ->
+                    new KeySource((String) e.getKey(), (String) e.getValue(), Source.THEME)).collect(toSet());
+
+            Map<Locale, Properties> realmLocalizationMessages = LocaleUtil.getRealmLocalizationTexts(realm, locale);
+            for (Locale currentLocale = locale; currentLocale != null; currentLocale = LocaleUtil.getParentLocale(currentLocale)) {
+                final List<KeySource> realmOverride = realmLocalizationMessages.get(currentLocale).entrySet().stream().map(e ->
+                        new KeySource((String) e.getKey(), (String) e.getValue(), Source.OVERRIDE)).collect(toList());
+                result.addAll(realmOverride);
+            }
+
+            return new ArrayList<>(result);
+        }
+        return theTheme.getEnhancedMessages(realm, locale).entrySet().stream().map(e ->
+                new KeySource((String) e.getKey(), (String) e.getValue())).collect(toList());
+    }
+}
+
+enum Source {
+    THEME,
+    OVERRIDE
+}
+class KeySource {
+    private String key;
+    private String value;
+    private Source source;
+
+    public KeySource(String key, String value) {
+        this.key = key;
+        this.value = value;
+    }
+
+    public KeySource(String key, String value, Source source) {
+        this(key, value);
+        this.source = source;
+    }
+
+    public String getKey() {
+        return key;
+    }
+
+    public String getValue() {
+        return value;
+    }
+
+    public Source getSource() {
+        return source;
+    }
+}

services/src/main/java/org/keycloak/services/util/LocaleUtil.java

@@ -200,7 +200,7 @@ public class LocaleUtil {
         return mergeGroupedMessages(locale, realmLocalizationMessages, themeMessages);
     }
 
-    private static Map<Locale, Properties> getRealmLocalizationTexts(RealmModel realm, Locale locale) {
+    public static Map<Locale, Properties> getRealmLocalizationTexts(RealmModel realm, Locale locale) {
         LinkedHashMap<Locale, Properties> groupedMessages = new LinkedHashMap<>();
 
         List<Locale> applicableLocales = getApplicableLocales(locale);