diff --git a/.gitignore b/.gitignore
index 015a031..0de9aaf 100644
--- a/.gitignore
+++ b/.gitignore
@@ -7,4 +7,3 @@ node_modules/
 .idea
 .sass-cache
 *.map
-js/lang.js
diff --git a/_build_js.sh b/_build_js.sh
index fea3428..32ff64a 100755
--- a/_build_js.sh
+++ b/_build_js.sh
@@ -2,8 +2,6 @@
 source "_build_common.sh"
 
 mkdir -p out/js
-echo 'Generating lang.js...'
-php ./dump_js_lang.php $@
 
 echo 'Processing JS...'
 npm run webpack
diff --git a/dump_js_lang.php b/dump_js_lang.php
deleted file mode 100755
index 80196de..0000000
--- a/dump_js_lang.php
+++ /dev/null
@@ -1,28 +0,0 @@
-<?php
-
-/* This script is run on demand to generate JS version of tr() */
-
-require_once __DIR__ . '/base.php';
-
-$selected = [
-	'wifi.connected_ip_is',
-	'wifi.not_conn',
-	'wifi.enter_passwd',
-	'term_nav.fullscreen',
-	'term_conn.connecting',
-	'term_conn.waiting_content',
-	'term_conn.disconnected',
-	'term_conn.waiting_server',
-	'term_conn.reconnecting'
-];
-
-$out = [];
-foreach ($selected as $key) {
-	$out[$key] = tr($key);
-}
-
-file_put_contents(__DIR__. '/js/lang.js',
-	"// Generated from PHP locale file\n" .
-	'let _tr = ' . json_encode($out, JSON_PRETTY_PRINT|JSON_UNESCAPED_UNICODE) . ";\n\n" .
-	"module.exports = function tr (key) { return _tr[key] || '?' + key + '?' }\n"
-);
diff --git a/js/lang.js b/js/lang.js
new file mode 100644
index 0000000..01bac93
--- /dev/null
+++ b/js/lang.js
@@ -0,0 +1,5 @@
+let data = require('locale-data')
+
+module.exports = function localize (key) {
+  return data[key] || `?${key}?`
+}
diff --git a/lang/_js-dump.php b/lang/_js-dump.php
new file mode 100755
index 0000000..411d6f2
--- /dev/null
+++ b/lang/_js-dump.php
@@ -0,0 +1,14 @@
+#! /usr/bin/env php
+<?php
+
+require_once __DIR__ . '/../base.php';
+
+$selected = array_slice($argv, 1);
+
+$output = [];
+
+foreach ($selected as $key) {
+  $output[$key] = tr($key);
+}
+
+fwrite(STDOUT, json_encode($output, JSON_UNESCAPED_UNICODE));
diff --git a/lang/_js-lang-loader.js b/lang/_js-lang-loader.js
new file mode 100644
index 0000000..8027abc
--- /dev/null
+++ b/lang/_js-lang-loader.js
@@ -0,0 +1,54 @@
+/*
+ * This is a Webpack loader that loads the language data by running
+ * dump_selected.php.
+ */
+
+const { spawnSync } = require('child_process')
+const path = require('path')
+const selectedKeys = require('./js-keys')
+
+module.exports = function (source) {
+  let child = spawnSync(path.resolve(__dirname, '_js-dump.php'), selectedKeys, {
+    timeout: 1000
+  })
+
+  let data
+  try {
+    data = JSON.parse(child.stdout.toString().trim())
+  } catch (err) {
+    console.error(`\x1b[31;1m[lang-loader] Failed to parse JSON:`)
+    console.error(child.stdout.toString().trim())
+    console.error(`\x1b[m`)
+
+    if (err) throw err
+  }
+
+  // adapted from webpack/loader-utils
+  let remainingRequest = this.remainingRequest
+  if (!remainingRequest) {
+    remainingRequest = this.loaders.slice(this.loaderIndex + 1)
+      .map(obj => obj.request)
+      .concat([this.resource]).join('!')
+  }
+
+  let currentRequest = this.currentRequest
+  if (!currentRequest) {
+    remainingRequest = this.loaders.slice(this.loaderIndex)
+      .map(obj => obj.request)
+      .concat([this.resource]).join('!')
+  }
+
+  let map = {
+    version: 3,
+    file: currentRequest,
+    sourceRoot: '',
+    sources: [remainingRequest],
+    sourcesContent: [source],
+    names: [],
+    mappings: 'AAAA;AAAA'
+  }
+
+  this.callback(null,
+    `/* Generated language file */\n` +
+    `module.exports=${JSON.stringify(data)}\n`, map)
+}
diff --git a/lang/js-keys.js b/lang/js-keys.js
new file mode 100644
index 0000000..967aa6f
--- /dev/null
+++ b/lang/js-keys.js
@@ -0,0 +1,12 @@
+// define language keys used by JS here
+module.exports = [
+  'wifi.connected_ip_is',
+  'wifi.not_conn',
+  'wifi.enter_passwd',
+  'term_nav.fullscreen',
+  'term_conn.connecting',
+  'term_conn.waiting_content',
+  'term_conn.disconnected',
+  'term_conn.waiting_server',
+  'term_conn.reconnecting'
+]
diff --git a/webpack.config.js b/webpack.config.js
index e332745..29ba3f4 100644
--- a/webpack.config.js
+++ b/webpack.config.js
@@ -20,6 +20,13 @@ plugins.push(new webpack.optimize.UglifyJsPlugin({
   sourceMap: devtool === 'source-map'
 }))
 
+// replace "locale-data" with path to locale data
+let locale = process.env.ESP_LANG || 'en'
+plugins.push(new webpack.NormalModuleReplacementPlugin(
+  /^locale-data$/,
+  path.resolve(`lang/${locale}.php`)
+))
+
 module.exports = {
   entry: './js',
   output: {
@@ -34,6 +41,10 @@ module.exports = {
           path.resolve(__dirname, 'node_modules')
         ],
         loader: 'babel-loader'
+      },
+      {
+        test: /lang\/.+?\.php$/,
+        loader: './lang/_js-lang-loader.js'
       }
     ]
   },