diff --git a/src/client/app/config.ts b/src/client/app/config.ts
index 7a441fdaa..6813c0127 100644
--- a/src/client/app/config.ts
+++ b/src/client/app/config.ts
@@ -12,7 +12,7 @@ export const hostname = address.hostname;
 export const url = address.origin;
 export const apiUrl = url + '/api';
 export const wsUrl = url.replace('http://', 'ws://').replace('https://', 'wss://') + '/streaming';
-export const lang = localStorage.getItem('lang');
+export const lang = localStorage.getItem('lang') || window.lang; // windowは後方互換性のため
 export const langs = _LANGS_;
 export const locale = JSON.parse(localStorage.getItem('locale'));
 export const copyright = _COPYRIGHT_;