diff --git a/src/Store.ts b/src/Store.ts
index f966c91e1..c9231895b 100644
--- a/src/Store.ts
+++ b/src/Store.ts
@@ -41,6 +41,7 @@ import type IndicatorImp from './component/Indicator'
 import type { IndicatorCreate, IndicatorFilter, IndicatorOverride } from './component/Indicator'
 import type OverlayImp from './component/Overlay'
 import { OVERLAY_ID_PREFIX, type OverlayCreate, type OverlayFigure, type OverlayFilter, type OverlayOverride } from './component/Overlay'
+import { getSupportedLocales } from './extension/i18n/index'
 import { getIndicatorClass } from './extension/indicator/index'
 import { getOverlayInnerClass } from './extension/overlay/index'
 import { getStyles as getExtensionStyles } from './extension/styles/index'
@@ -481,6 +482,11 @@ export default class StoreImp implements Store {
   }
 
   setLocale(locale: string): void {
+    if (!getSupportedLocales().includes(locale)) {
+      logWarn('', '', `Locale ${locale} is not supported, fallback to en-US.`)
+      this._locale = 'en-US'
+      return
+    }
     this._locale = locale
   }
 
diff --git a/src/extension/i18n/index.ts b/src/extension/i18n/index.ts
index 9090ff134..a199d446e 100644
--- a/src/extension/i18n/index.ts
+++ b/src/extension/i18n/index.ts
@@ -30,7 +30,7 @@ function getSupportedLocales(): string[] {
 }
 
 function i18n(key: string, locale: string): string {
-  return locales[locale][key] ?? key
+  return locales[locale]?.[key] ?? key
 }
 
 export { getSupportedLocales, i18n, registerLocale }