Set locale_default at initial admin creation too.

app/assets/javascripts/app/controllers/getting_started.coffee

@@ -240,6 +240,9 @@ class Admin extends App.WizardFullScreen
 
   relogin: (data, status, xhr) =>
     @log 'notice', 'relogin:success', data
+    callback = ->
+      App.Setting.set('locale_default', App.i18n.detectBrowserLocale())
+    App.Setting.fetchFull(callback)
     App.Event.trigger 'notify:removeall'
     @navigate 'getting_started/base'
 

db/migrate/20171206000001_setting_default_locale2.rb

@@ -1,13 +1,20 @@
-class SettingDefaultLocale < ActiveRecord::Migration[5.1]
+class SettingDefaultLocale2 < ActiveRecord::Migration[5.1]
   def up
 
     # return if it's a new setup
     return if !Setting.find_by(name: 'system_init_done')
 
+    setting = Setting.find_by(name: 'locale_default')
+    if setting
+      setting.area = 'System::Branding'
+      setting.preferences[:prio] = 8
+      setting.save!
+    end
+
     Setting.create_if_not_exists(
       title: 'Locale',
       name: 'locale_default',
-      area: 'System::Base',
+      area: 'System::Branding',
       description: 'Defines the system default language.',
       options: {
         form: [
@@ -18,6 +25,7 @@ class SettingDefaultLocale < ActiveRecord::Migration[5.1]
       },
       state: 'en-us',
       preferences: {
+        prio: 8,
         controller: 'SettingsAreaItemDefaultLocale',
         permission: ['admin.system'],
       },

db/seeds/settings.rb

@@ -156,6 +156,26 @@ Setting.create_if_not_exists(
   },
   frontend: true
 )
+Setting.create_if_not_exists(
+  title: 'Locale',
+  name: 'locale_default',
+  area: 'System::Branding',
+  description: 'Defines the system default language.',
+  options: {
+    form: [
+      {
+        name: 'locale_default',
+      }
+    ],
+  },
+  state: 'en-us',
+  preferences: {
+    prio: 8,
+    controller: 'SettingsAreaItemDefaultLocale',
+    permission: ['admin.system'],
+  },
+  frontend: true
+)
 Setting.create_or_update(
   title: 'Pretty Date',
   name: 'pretty_date_format',
@@ -183,25 +203,6 @@ Setting.create_or_update(
   state: 'relative',
   frontend: true
 )
-Setting.create_if_not_exists(
-  title: 'Locale',
-  name: 'locale_default',
-  area: 'System::Base',
-  description: 'Defines the system default language.',
-  options: {
-    form: [
-      {
-        name: 'locale_default',
-      }
-    ],
-  },
-  state: 'en-us',
-  preferences: {
-    controller: 'SettingsAreaItemDefaultLocale',
-    permission: ['admin.system'],
-  },
-  frontend: true
-)
 options = {}
 (10..99).each do |item|
   options[item] = item