diff --git a/background.js b/background.js
index ed142c7..f569bbb 100644
--- a/background.js
+++ b/background.js
@@ -13,8 +13,9 @@ import * as rwhCompose from './modules/compose.mjs';
 import * as rwhTabs from './modules/tabs.mjs';
 import * as rwhSettings from './modules/settings.mjs';
 import * as rwhAccounts from './modules/accounts.mjs';
+import * as rwhI18n from './modules/headers-i18n.mjs';
 
-messenger.runtime.onInstalled.addListener(async function(details) {
+messenger.runtime.onInstalled.addListener(async function (details) {
     // About 'details' argument
     // Refer here: https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/WebExtensions/API/runtime/onInstalled
     rwhLogger.debug(details);
@@ -22,18 +23,28 @@ messenger.runtime.onInstalled.addListener(async function(details) {
     rwhSettings.setAccountDefaults(accounts);
 });
 
-messenger.accounts.onCreated.addListener(async function(id, account){
+messenger.accounts.onCreated.addListener(async function (id, account) {
     rwhLogger.debug('onCreated', id, account);
     if (account.type === 'imap' || account.type === 'pop3') {
         rwhSettings.setDefault(`${id}.enabled`, true);
     }
 });
 
-messenger.accounts.onDeleted.addListener(async function(id){
+messenger.accounts.onDeleted.addListener(async function (id) {
     rwhLogger.debug('onDeleted', id);
     rwhSettings.remove(`${id}.enabled`);
 });
 
+async function detectLocaleAndSetAsDefault() {
+    let uiLocale = messenger.i18n.getUILanguage();
+    let selected = rwhI18n.i18n.lang[uiLocale];
+    let currentLocale = await rwhSettings.getHeaderLocale();
+    rwhLogger.debug('currentLocale:', currentLocale, 'uiLocale:', uiLocale, 'selected:', selected);
+    if (selected !== 'undefined' && currentLocale !== uiLocale) {
+        await rwhSettings.set('header.locale', uiLocale);
+    }
+}
+
 async function init() {
     await rwhSettings.setDefaults();
 
@@ -43,11 +54,12 @@ async function init() {
         await rwhCompose.process(tab);
     });
 
+    await detectLocaleAndSetAsDefault();
 }
 
 try {
     init();
     rwhLogger.info('Addon loaded successfully');
-} catch(e) {
+} catch (e) {
     rwhLogger.error(e);
 }