diff --git a/js/i18n.js b/js/i18n.js
index 4ec0c183c1e1..de7330497c1a 100644
--- a/js/i18n.js
+++ b/js/i18n.js
@@ -1,5 +1,7 @@
 /* eslint-env node */
 
+'use strict';
+
 exports.setup = (locale, messages) => {
   if (!locale) {
     throw new Error('i18n: locale parameter is required');