SSR: Add meta description tag on the Signup section (#95013)

* SSR: Add meta description tag on the Signup section

* Remove previous description and robots meta tags

* Setup locale data only for English and Mag-16 locales

* Pass required params to ssrSetupLocale

* Fix indexing the localized main pages for Mag-16 locales

* Improve comment

* Update the noindex comment

* Use `isMagnificentLocale` utility

client/signup/index.node.js

@@ -1,4 +1,11 @@
-import { getLanguage, getLanguageRouteParam } from '@automattic/i18n-utils';
+import {
+	getLanguage,
+	getLanguageRouteParam,
+	isDefaultLocale,
+	isMagnificentLocale,
+} from '@automattic/i18n-utils';
+import defaultI18n from 'i18n-calypso';
+import { ssrSetupLocale } from 'calypso/controller';
 import { setDocumentHeadMeta } from 'calypso/state/document-head/actions';
 import { getDocumentHeadMeta } from 'calypso/state/document-head/selectors';
 
@@ -24,19 +31,49 @@ function setUpLocale( context, next ) {
 		context.lang = context.params.lang;
 	}
 
+	const shouldSetupLocaleData =
+		isDefaultLocale( context.lang ) || isMagnificentLocale( context.lang );
+
+	if ( shouldSetupLocaleData ) {
+		return ssrSetupLocale( context, next );
+	}
+
 	next();
 }
 
 // Set up meta tags.
 function setupMetaTags( context, next ) {
-	// All `/start/*` sub-pages should be noindex. See 3065-gh-Automattic/martech.
-	if ( ! /^\/start\/?$/.test( context.pathname ) ) {
-		const meta = getDocumentHeadMeta( context.store.getState() ).concat( {
+	const i18n = context.i18n || defaultI18n;
+	const translate = i18n.translate.bind( i18n );
+
+	/**
+	 * Get the meta tags, excluding `description` and `robots` meta items, to prevent duplications.
+	 */
+	const meta = getDocumentHeadMeta( context.store.getState() ).filter(
+		( { name } ) => name !== 'description' && name !== 'robots'
+	);
+
+	meta.push( {
+		name: 'description',
+		content: translate(
+			'Sign up for a free WordPress.com account to start building your new website. Get access to powerful tools and customizable designs to bring your ideas to life.'
+		),
+	} );
+
+	const pathSegments = context.pathname.replace( /^[/]|[/]$/g, '' ).split( '/' );
+	const hasQueryString = Object.keys( context.query ).length > 0;
+	const hasMag16LocaleParam = isMagnificentLocale( context.params?.lang );
+
+	/**
+	 * Only the main `/start` and `/start/[mag-16-locale]` pages should be indexed. See 3065-gh-Automattic/martech.
+	 */
+	if ( hasQueryString || pathSegments.length > ( hasMag16LocaleParam ? 2 : 1 ) ) {
+		meta.push( {
 			name: 'robots',
 			content: 'noindex',
 		} );
-		context.store.dispatch( setDocumentHeadMeta( meta ) );
 	}
 
+	context.store.dispatch( setDocumentHeadMeta( meta ) );
 	next();
 }