diff --git a/client-addon/src/locales/en.json b/client-addon/src/locales/en.json
index 408b2d2..f8d0cb4 100644
--- a/client-addon/src/locales/en.json
+++ b/client-addon/src/locales/en.json
@@ -4,6 +4,19 @@
       "vue-i18n": {
         "title": "Project Localizations",
         "tooltip": "Localizations",
+        "config": {
+          "description": "Settings of I18n",
+          "prompts": {
+            "locale": {
+              "message": "Locale",
+              "description": "Locale of project localization"
+            },
+            "fallbackLocale": {
+              "message": "Fallback Locale",
+              "description": "Fallback locale of project localization"
+            }
+          }
+        },
         "notification": {
           "title": "Vue I18n",
           "message": "Added a {locale}"
diff --git a/client-addon/src/locales/ja.json b/client-addon/src/locales/ja.json
index 7fe62e8..81fdd92 100644
--- a/client-addon/src/locales/ja.json
+++ b/client-addon/src/locales/ja.json
@@ -2,6 +2,21 @@
   "org": {
     "kazupon": {
       "vue-i18n": {
+        "title": "プロジェクトローカライゼーション",
+        "tooltip": "ローカライゼーション",
+        "config": {
+          "description": "I18n の設定",
+          "prompts": {
+            "locale": {
+              "message": "ロケール",
+              "description": "プロジェクトローカライズゼーションのロケール"
+            },
+            "fallbackLocale": {
+              "message": "フォールバックロケール",
+              "description": "プロジェクトローカライズゼーションのフォールバックロケール"
+            }
+          }
+        },
         "editor": {
           "messages": "メッセージ",
           "paths": "パス"
@@ -48,9 +63,7 @@
             "title": "確認"
           },
           "placeholder": "パスを更新"
-        },
-        "title": "プロジェクトローカライゼーション",
-        "tooltip": "ローカライゼーション"
+        }
       }
     }
   }
diff --git a/generator/index.js b/generator/index.js
index e5cddc9..e6ace84 100644
--- a/generator/index.js
+++ b/generator/index.js
@@ -4,28 +4,9 @@ const {
   exists,
   mkdir,
   writeFile,
-  readFile
+  readEnv,
+  buildEnvContent
 } = require('../utils')
-const dotenv = require('dotenv')
-
-function readEnv (path) {
-  let ret = {}
-  try {
-    ret = dotenv.parse(Buffer.from(readFile(path)))
-  } catch (e) {
-    console.warn('readEnv error:', e.message)
-    ret = {}
-  }
-  return ret
-}
-
-function buildEnvContent (values) {
-  let content = ''
-  Object.keys(values).forEach(key => {
-    content += `${key}=${values[key]}\n`
-  })
-  return content
-}
 
 module.exports = (api, options, rootOptions) => {
   const { locale, fallbackLocale, localeDir, enableInSFC } = options
diff --git a/ui.js b/ui.js
index e4d02d1..4c8d33c 100644
--- a/ui.js
+++ b/ui.js
@@ -4,7 +4,13 @@ const path = require('path')
 const deepmerge = require('deepmerge')
 const flatten = require('flat')
 const unflatten = require('flat').unflatten
-const { isObject, readEnv, sortObject } = require('./utils')
+const {
+  isObject,
+  readEnv,
+  buildEnvContent,
+  writeFile,
+  sortObject
+} = require('./utils')
 const i18n = require('./i18n')
 
 function getValuesFromPath (path, messages) {
@@ -73,6 +79,7 @@ function writeLocaleMessages (targetPath, locale, messages, order) {
 
 module.exports = api => {
   const { getSharedData, setSharedData, watchSharedData } = api.namespace('org.kazupon.vue-i18n.')
+  let clientLocale = 'en'
 
   function setupAddon (path, options) {
     debug(`setupAddon: path -> ${path}, options -> ${options}`)
@@ -236,7 +243,6 @@ module.exports = api => {
       setSharedData('locales', locales)
       setSharedData('current', locale)
 
-      const clientLocale = getSharedData('clientLocale').value
       debug('add-locale-action: clientLocale', clientLocale)
       api.notify({
         title: i18n.t('org.kazupon.vue-i18n.notification.title', clientLocale),
@@ -245,6 +251,45 @@ module.exports = api => {
       })
     })
 
+    api.describeConfig({
+      id: 'org.kazupon.vue-i18n.config',
+      name: 'Vue I18n',
+      description: 'org.kazupon.vue-i18n.config.description',
+      icon: '/_plugin/vue-cli-plugin-i18n/nav-logo.svg',
+      onRead: ({ data, cwd }) => {
+        const env = readEnv(`${cwd}/.env`)
+        const currentLocale = env['VUE_APP_I18N_LOCALE']
+        const defaultLocale = env['VUE_APP_I18N_FALLBACK_LOCALE']
+        debug('onRead', data, clientLocale, currentLocale, defaultLocale)
+        return {
+          prompts: [{
+            type: 'input',
+            name: 'locale',
+            message: 'org.kazupon.vue-i18n.config.prompts.locale.message',
+            description: 'org.kazupon.vue-i18n.config.prompts.locale.description',
+            value: currentLocale || 'en'
+          }, {
+            type: 'input',
+            name: 'fallbackLocale',
+            message: 'org.kazupon.vue-i18n.config.prompts.fallbackLocale.message',
+            description: 'org.kazupon.vue-i18n.config.prompts.fallbackLocale.description',
+            value: defaultLocale || 'en'
+          }]
+        }
+      },
+      onWrite: ({ answers, data, cwd }) => {
+        debug('onWrite', cwd, answers, data)
+        const envPath = `${cwd}/.env`
+        const env = readEnv(envPath)
+        const { locale, fallbackLocale } = answers
+        env['VUE_APP_I18N_LOCALE'] = locale
+        env['VUE_APP_I18N_FALLBACK_LOCALE'] = fallbackLocale
+        if (!writeFile(envPath, buildEnvContent(env))) {
+          console.error('onWrite: failed env variables')
+        }
+      }
+    })
+
     api.addView({
       id: 'org.kazupon.vue-i18n.views.entry',
       name: 'org.kazupon.vue-i18n.routes.entry',
@@ -272,5 +317,6 @@ module.exports = api => {
 
   watchSharedData('clientLocale', (val, old) => {
     debug('watch `clientLocale`:', val, old)
+    clientLocale = val
   })
 }
diff --git a/utils.js b/utils.js
index ba4db54..bbe651e 100644
--- a/utils.js
+++ b/utils.js
@@ -70,6 +70,14 @@ function readEnv (path) {
   return ret
 }
 
+function buildEnvContent (values) {
+  let content = ''
+  Object.keys(values).forEach(key => {
+    content += `${key}=${values[key]}\n`
+  })
+  return content
+}
+
 function sortObject (obj, order = 'asc') {
   const keys = Object.keys(obj)
   const sortedKeys = order === 'asc' ? keys.sort() : keys.reverse()
@@ -94,5 +102,6 @@ module.exports = {
   writeFile,
   readFile,
   readEnv,
+  buildEnvContent,
   sortObject
 }