diff --git a/src/web/app/init.js b/src/web/app/init.js
index cb661c2595..5a6899ed4f 100644
--- a/src/web/app/init.js
+++ b/src/web/app/init.js
@@ -21,6 +21,11 @@ require('./common/tags');
 
 console.info(`Misskey v${VERSION} (葵 aoi)`);
 
+{ // Set lang attr
+	const html = document.documentElement;
+	html.setAttribute('lang', LANG);
+}
+
 { // Set description meta tag
 	const head = document.getElementsByTagName('head')[0];
 	const meta = document.createElement('meta');
diff --git a/webpack/plugins/const.ts b/webpack/plugins/const.ts
index ccfcb45260..f64160b01a 100644
--- a/webpack/plugins/const.ts
+++ b/webpack/plugins/const.ts
@@ -7,7 +7,8 @@ import * as webpack from 'webpack';
 import version from '../../src/version';
 const constants = require('../../src/const.json');
 
-export default () => new webpack.DefinePlugin({
+export default lang => new webpack.DefinePlugin({
 	VERSION: JSON.stringify(version),
+	LANG: JSON.stringify(lang),
 	THEME_COLOR: JSON.stringify(constants.themeColor)
 });
diff --git a/webpack/plugins/index.ts b/webpack/plugins/index.ts
index d5191f1555..345af7df9e 100644
--- a/webpack/plugins/index.ts
+++ b/webpack/plugins/index.ts
@@ -8,9 +8,9 @@ import banner from './banner';
 const env = process.env.NODE_ENV;
 const isProduction = env === 'production';
 
-export default version => {
+export default (version, lang) => {
 	const plugins = [
-		constant(),
+		constant(lang),
 		new StringReplacePlugin(),
 		hoist()
 	];
diff --git a/webpack/webpack.config.ts b/webpack/webpack.config.ts
index 066df18157..97782a4102 100644
--- a/webpack/webpack.config.ts
+++ b/webpack/webpack.config.ts
@@ -32,7 +32,7 @@ module.exports = langs.map(([lang, locale]) => {
 		name,
 		entry,
 		module: module_(lang, locale),
-		plugins: plugins(version),
+		plugins: plugins(version, lang),
 		output
 	};
 });