If user profile doesn't contain language setting, default to his Google account settings.

chrome/browser/profiles/profile_impl.cc

Index: chrome/browser/profiles/profile_impl.cc
diff --git a/chrome/browser/profiles/profile_impl.cc b/chrome/browser/profiles/profile_impl.cc
index c3650e8ba514879259e8d40b907acc558da8e9aa..aef1dc6c12498f255da45dcb93d1d141e445e000 100644
--- a/chrome/browser/profiles/profile_impl.cc
+++ b/chrome/browser/profiles/profile_impl.cc
@@ -1042,7 +1042,9 @@ void ProfileImpl::ChangeAppLocale(
         // (2) on next login we assume that synchronization is already completed
         //     and we may finalize initialization.
         GetPrefs()->SetString(prefs::kApplicationLocaleBackup, cur_locale);
-        if (!backup_locale.empty())
+        if (!new_locale.empty())
+          GetPrefs()->SetString(prefs::kApplicationLocale, new_locale);
+        else if (!backup_locale.empty())
           GetPrefs()->SetString(prefs::kApplicationLocale, backup_locale);
         do_update_pref = false;
       }