Use extension api to get initial locale.

app/scripts/background.js

@@ -19,7 +19,7 @@ const setupRaven = require('./lib/setupRaven')
 const reportFailedTxToSentry = require('./lib/reportFailedTxToSentry')
 const setupMetamaskMeshMetrics = require('./lib/setupMetamaskMeshMetrics')
 const EdgeEncryptor = require('./edge-encryptor')
-
+const getFirstPreferredLangCode = require('./lib/get-first-preferred-lang-code')
 
 const STORAGE_KEY = 'metamask-config'
 const METAMASK_DEBUG = 'GULP_METAMASK_DEBUG'
@@ -58,7 +58,8 @@ setupMetamaskMeshMetrics()
 
 async function initialize () {
   const initState = await loadStateFromPersistence()
-  await setupController(initState)
+  const initLangCode = await getFirstPreferredLangCode()
+  await setupController(initState, initLangCode)
   log.debug('MetaMask initialization complete.')
 }
 
@@ -90,11 +91,10 @@ async function loadStateFromPersistence () {
   return versionedData.data
 }
 
-function setupController (initState) {
+function setupController (initState, initLangCode) {
   //
   // MetaMask Controller
   //
-
   const controller = new MetamaskController({
     // User confirmation callbacks:
     showUnconfirmedMessage: triggerUi,
@@ -102,6 +102,8 @@ function setupController (initState) {
     showUnapprovedTx: triggerUi,
     // initial state
     initState,
+    // initial locale code
+    initLangCode,
     // platform specific api
     platform,
     encryptor: isEdge ? new EdgeEncryptor() : undefined,

app/scripts/controllers/preferences.js

@@ -11,7 +11,7 @@ class PreferencesController {
       tokens: [],
       useBlockie: false,
       featureFlags: {},
-      currentLocale: 'ja',
+      currentLocale: opts.initLangCode,
     }, opts.initState)
     this.store = new ObservableStore(initState)
   }

app/scripts/lib/get-first-preferred-lang-code.js

@@ -0,0 +1,18 @@
+const fs = require('fs')
+const path = require('path')
+const extension = require('extensionizer')
+const promisify = require('pify')
+
+const existingLocaleCodes = fs.readdirSync(path.join(__dirname, '..', '..', '_locales'))
+
+async function getFirstPreferredLangCode () {
+  const userPreferredLocaleCodes = await promisify(
+    extension.i18n.getAcceptLanguages,
+    { errorFirst: false }
+  )().catch(err => console.log('err123', err))
+  const firstPreferredLangCode = userPreferredLocaleCodes.find(code => existingLocaleCodes.includes(code))
+  // const firstPreferredLangCode = userPreferredLocaleCodes[0]
+  return firstPreferredLangCode || 'en'
+}
+
+module.exports = getFirstPreferredLangCode

app/scripts/metamask-controller.js

@@ -57,7 +57,6 @@ module.exports = class MetamaskController extends EventEmitter {
     this.defaultMaxListeners = 20
 
     this.sendUpdate = debounce(this.privateSendUpdate.bind(this), 200)
-
     this.opts = opts
     const initState = opts.initState || {}
     this.recordFirstTimeInfo(initState)
@@ -82,6 +81,7 @@ module.exports = class MetamaskController extends EventEmitter {
     // preferences controller
     this.preferencesController = new PreferencesController({
       initState: initState.PreferencesController,
+      initLangCode: opts.initLangCode,
     })
 
     // currency controller

package.json

@@ -141,6 +141,7 @@
     "promise-filter": "^1.1.0",
     "promise-to-callback": "^1.0.0",
     "pump": "^3.0.0",
+    "pify": "^3.0.0",
     "pumpify": "^1.3.4",
     "qrcode-npm": "0.0.3",
     "ramda": "^0.24.1",