fix(client): PWAでlangがnullになる現象の応急処置

#10202

packages/backend/src/server/web/boot.js

@@ -61,6 +61,10 @@
 			renderError('META_FETCH_V');
 			return;
 		}
+
+		// for https://github.com/misskey-dev/misskey/issues/10202
+		if (lang == null || lang.toString == null || lang.toString() === 'null') lang = 'en-US';
+
 		const localRes = await window.fetch(`/assets/locales/${lang}.${v}.json`);
 		if (localRes.status === 200) {
 			localStorage.setItem('lang', lang);