diff --git a/src/build/i18n.ts b/src/build/i18n.ts
index 35204c34a4..2790191191 100644
--- a/src/build/i18n.ts
+++ b/src/build/i18n.ts
@@ -63,6 +63,8 @@ export default class Replacer {
 			key = key.substr(1);
 		}
 
+		if (ctx && ctx.lang) this.lang = ctx.lang;
+
 		if (match[0] == '"') {
 			return '"' + this.get(name, key).replace(/"/g, '\\"') + '"';
 		} else if (match[0] == "'") {
diff --git a/src/client/app/boot.js b/src/client/app/boot.js
index 2675fa233a..12b0d220a9 100644
--- a/src/client/app/boot.js
+++ b/src/client/app/boot.js
@@ -31,11 +31,9 @@
 
 	// Detect the user language
 	// Note: The default language is Japanese
-	//let lang = navigator.language.split('-')[0];
-	//if (!/^(en|ja)$/.test(lang)) lang = 'ja';
-	//if (localStorage.getItem('lang')) lang = localStorage.getItem('lang');
-	//if (ENV != 'production') lang = 'ja';
-	const lang = 'ja';
+	let lang = navigator.language.split('-')[0];
+	if (!/^(en|ja)$/.test(lang)) lang = 'ja';
+	if (localStorage.getItem('lang')) lang = localStorage.getItem('lang');
 
 	// Detect the user agent
 	const ua = navigator.userAgent.toLowerCase();
diff --git a/webpack.config.ts b/webpack.config.ts
index b0b06c7392..bc876e067d 100644
--- a/webpack.config.ts
+++ b/webpack.config.ts
@@ -42,7 +42,7 @@ const langs = Object.keys(locales);
 
 const entries = process.env.NODE_ENV == 'production'
 	? langs.map(l => [l, false]).concat(langs.map(l => [l, true]))
-	: [['ja', false]];
+	: langs.map(l => [l, false]);
 
 module.exports = entries.map(x => {
 	const [lang, isProduction] = x;
@@ -144,7 +144,8 @@ module.exports = entries.map(x => {
 					query: {
 						search: i18nReplacer.pattern.toString(),
 						replace: 'i18nReplacement',
-						i18n: true
+						i18n: true,
+						lang
 					}
 				}, {
 					loader: 'replace',
@@ -216,7 +217,8 @@ module.exports = entries.map(x => {
 					query: {
 						search: i18nReplacer.pattern.toString(),
 						replace: 'i18nReplacement',
-						i18n: true
+						i18n: true,
+						lang
 					}
 				}, {
 					loader: 'replace',
diff --git a/webpack/loaders/replace.js b/webpack/loaders/replace.js
index 9897fe37d5..0326dcdab3 100644
--- a/webpack/loaders/replace.js
+++ b/webpack/loaders/replace.js
@@ -11,7 +11,8 @@ module.exports = function(src) {
 	const g = search[search.length - 1] == 'g';
 	const file = this.resourcePath.replace(/\\/g, '/');
 	const replace = options.i18n ? global[options.replace].bind(null, {
-		src: file
+		src: file,
+		lang: options.lang
 	}) : global[options.replace];
 	if (typeof search != 'string' || search.length == 0) console.error('invalid search');
 	if (typeof replace != 'function') console.error('invalid replacer:', replace, this.request);