Support passing in locale option to init() (#11760)

Closes #11759

docs/documentation/securing_apps/topics/oidc/javascript-adapter.adoc

@@ -375,6 +375,7 @@ reference link:{adminguide_link}#_client_scopes[Client scopes] defined on a part
 always added to the list of scopes by the adapter. For example, if you enter the scope options `address phone`, then the request
 to {project_name} will contain the scope parameter `scope=openid address phone`.
 * messageReceiveTimeout - Set a timeout in milliseconds for waiting for message responses from the Keycloak server. This is used, for example, when waiting for a message during 3rd party cookies check. The default value is 10000.
+* locale - When onLoad is 'login-required', sets the 'ui_locales' query param in compliance with https://openid.net/specs/openid-connect-core-1_0.html#AuthRequest[section 3.1.2.1 of the OIDC 1.0 specification].
 
 Returns a promise that resolves when initialization completes.
 

js/libs/keycloak-js/dist/keycloak.d.ts

@@ -195,6 +195,12 @@ export interface KeycloakInitOptions {
 	 * @default 10000
 	 */
 	messageReceiveTimeout?: number
+
+	/**
+	 * When onLoad is 'login-required', sets the 'ui_locales' query param in compliance with section 3.1.2.1
+	 * of the OIDC 1.0 specification.
+	 */
+	locale?: string;
 }
 
 export interface KeycloakLoginOptions {

js/libs/keycloak-js/src/keycloak.js

@@ -176,6 +176,9 @@ function Keycloak (config) {
                     options.prompt = 'none';
                 }
 
+                if (initOptions && initOptions.locale) {
+                    options.locale = initOptions.locale;
+                }
                 kc.login(options).then(function () {
                     initPromise.setSuccess();
                 }).catch(function (error) {