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..f07228fcdc7753b966567febee8179cdeb7e8584 100644
--- a/chrome/browser/profiles/profile_impl.cc
+++ b/chrome/browser/profiles/profile_impl.cc
@@ -29,6 +29,7 @@
 #include "chrome/browser/bookmarks/bookmark_model_factory.h"
 #include "chrome/browser/browser_process.h"
 #include "chrome/browser/chrome_notification_types.h"
+#include "chrome/browser/chromeos/login/language_switch_menu.h"
 #include "chrome/browser/content_settings/cookie_settings.h"
 #include "chrome/browser/content_settings/host_content_settings_map.h"
 #include "chrome/browser/download/chrome_download_manager_delegate.h"
@@ -361,6 +362,9 @@ ProfileImpl::ProfileImpl(
       host_content_settings_map_(NULL),
       last_session_exit_type_(EXIT_NORMAL),
       start_time_(Time::Now()),
+#if defined(OS_CHROMEOS)
+      is_created_(false),
+#endif
       delegate_(delegate),
       predictor_(NULL) {
   TRACE_EVENT0("browser", "ProfileImpl::ctor")
@@ -987,6 +991,10 @@ void ProfileImpl::EnsureSessionServiceCreated() {
 #endif
 
 #if defined(OS_CHROMEOS)
+void ProfileImpl::MarkCreated() {
+  is_created_ = true;
+}
+
 void ProfileImpl::ChangeAppLocale(
     const std::string& new_locale, AppLocaleChangedVia via) {
   if (new_locale.empty()) {
@@ -1042,7 +1050,9 @@ 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;
       }
@@ -1062,6 +1072,43 @@ void ProfileImpl::ChangeAppLocale(
     local_state->SetString(prefs::kOwnerLocale, new_locale);
 }
 
+void ProfileImpl::SetGPlusProfileLocale(const std::string& gplus_locale) {
+  gplus_locale_.reset(new std::string);
+  // Ignore result
+  l10n_util::CheckAndResolveLocale(gplus_locale, gplus_locale_.get());

[jungshik at Google, 2013/08/26 16:42:50]

This does not take into account the preferred language list in the Google user
profile. If a user's primary language is not supported by Chrome OS (let's say,
"Foo") but one of languages in the fallback list in the user's Google profile
(e.g. French) is supported by Chrome, we have to pick it up instead of falling
back to the universal (hard-coded) fallback ('en-US'). 

The Linux locale fallback has a similar mechanism because 'LANGUAGE' environment
variable can have a list of languages (e.g. 'foo:fr-CA:fr-FR').  

If you don't want to do now, at least add TODO comment about this. 

[Alexander Alekseev, 2013/09/06 19:52:08]

I like the idea, but I couldn't find "list of languages" in API.
https://developers.google.com/+/api/latest/people
- doesn't list anything alike.

[jungshik at Google, 2013/09/18 08:50:04]

Thanks for digging that up. I've alerted an engineer working on the language
setting of Google users. He's not aware of this API.

+  RespectLocalePreference();
+}
+
+void ProfileImpl::RespectLocalePreference() {
+  PrefService* prefs = GetPrefs();
+  DCHECK(prefs != NULL);
+  if (g_browser_process == NULL)
+    return;
+
+  if (!is_created_)
+    return;
+
+  if (gplus_locale_ == NULL)
+    return;
+
+  std::string pref_locale = prefs->GetString(prefs::kApplicationLocale);
+  if (pref_locale.empty())
+    pref_locale = prefs->GetString(prefs::kApplicationLocaleBackup);
+  if (pref_locale.empty())
+    pref_locale = *gplus_locale_;
+  if (pref_locale.empty())
+    pref_locale = g_browser_process->GetApplicationLocale();
+  DCHECK(!pref_locale.empty());
+  ChangeAppLocale(pref_locale, APP_LOCALE_CHANGED_VIA_LOGIN);
+  // Here we don't enable keyboard layouts. Input methods are set up when
+  // the user first logs in. Then the user may customize the input methods.
+  // Hence changing input methods here, just because the user's UI language
+  // is different from the login screen UI language, is not desirable. Note
+  // that input method preferences are synced, so users can use their
+  // farovite input methods as soon as the preferences are synced.
+  chromeos::LanguageSwitchMenu::SwitchLanguage(pref_locale);
+}
+
 void ProfileImpl::OnLogin() {
   if (locale_change_guard_ == NULL)
     locale_change_guard_.reset(new chromeos::LocaleChangeGuard(this));