fix: respect system language preferences on Win/macOS (#23247)

This commit fixes https://github.com/electron/electron/issues/18829

Previously the full preferences set to OS was not given to Chromium.

Also, this commit improves fallback font selection for CJK text.
Chromium uses browser languages to determine fallback fonts on Windows,
especially kanji/han characters in CJK.

For instance, when user sets 'en-US, ja-JP' to Accept-Language,
while Chromium chooses Japanese font for kanji text, but Electron
chooses Chinese font.  This is because only the first language was given
to Accept-Language on Electron.

This patch is based on https://github.com/electron/electron/pull/15532

Co-authored-by: Nitish Sakhawalkar <nitsakh@icloud.com>
Co-authored-by: Kasumi Hanazuki <kasumi@rollingapple.net>

Co-authored-by: Nitish Sakhawalkar <nitsakh@icloud.com>
Co-authored-by: Kasumi Hanazuki <kasumi@rollingapple.net>

filenames.gni

@@ -543,6 +543,10 @@ filenames = {
     "shell/common/key_weak_map.h",
     "shell/common/keyboard_util.cc",
     "shell/common/keyboard_util.h",
+    "shell/common/language_util.h",
+    "shell/common/language_util_linux.cc",
+    "shell/common/language_util_mac.mm",
+    "shell/common/language_util_win.cc",
     "shell/common/mac/main_application_bundle.h",
     "shell/common/mac/main_application_bundle.mm",
     "shell/common/mouse_util.cc",

shell/browser/api/electron_api_web_contents.cc

@@ -89,6 +89,7 @@
 #include "shell/common/gin_converters/value_converter.h"
 #include "shell/common/gin_helper/dictionary.h"
 #include "shell/common/gin_helper/object_template_builder.h"
+#include "shell/common/language_util.h"
 #include "shell/common/mouse_util.h"
 #include "shell/common/node_includes.h"
 #include "shell/common/options_switches.h"
@@ -100,6 +101,7 @@
 #include "third_party/blink/public/mojom/frame/find_in_page.mojom.h"
 #include "third_party/blink/public/mojom/frame/fullscreen.mojom.h"
 #include "third_party/blink/public/mojom/messaging/transferable_message.mojom.h"
+#include "third_party/blink/public/mojom/renderer_preferences.mojom.h"
 #include "ui/base/cursor/cursor.h"
 #include "ui/base/mojom/cursor_type.mojom-shared.h"
 #include "ui/display/screen.h"
@@ -121,7 +123,6 @@
 #endif
 
 #if defined(OS_LINUX) || defined(OS_WIN)
-#include "third_party/blink/public/mojom/renderer_preferences.mojom.h"
 #include "ui/gfx/font_render_params.h"
 #endif
 
@@ -535,7 +536,22 @@ void WebContents::InitWithSessionAndOptions(
   managed_web_contents()->GetView()->SetDelegate(this);
 
   auto* prefs = web_contents()->GetMutableRendererPrefs();
-  prefs->accept_languages = g_browser_process->GetApplicationLocale();
+
+  // Collect preferred languages from OS and browser process. accept_languages
+  // effects HTTP header, navigator.languages, and CJK fallback font selection.
+  //
+  // Note that an application locale set to the browser process might be
+  // different with the one set to the preference list.
+  // (e.g. overridden with --lang)
+  std::string accept_languages =
+      g_browser_process->GetApplicationLocale() + ",";
+  for (auto const& language : electron::GetPreferredLanguages()) {
+    if (language == g_browser_process->GetApplicationLocale())
+      continue;
+    accept_languages += language + ",";
+  }
+  accept_languages.pop_back();
+  prefs->accept_languages = accept_languages;
 
 #if defined(OS_LINUX) || defined(OS_WIN)
   // Update font settings.

shell/common/language_util.h

@@ -0,0 +1,26 @@
+// Copyright (c) 2020 GitHub, Inc.
+// Use of this source code is governed by the MIT license that can be
+// found in the LICENSE file.
+
+#ifndef SHELL_COMMON_LANGUAGE_UTIL_H_
+#define SHELL_COMMON_LANGUAGE_UTIL_H_
+
+#include <string>
+#include <vector>
+
+#include "base/strings/string16.h"
+
+namespace electron {
+
+// Return a list of user preferred languages from OS. The list doesn't include
+// overrides from command line arguments.
+std::vector<std::string> GetPreferredLanguages();
+
+#if defined(OS_WIN)
+bool GetPreferredLanguagesUsingGlobalization(
+    std::vector<base::string16>* languages);
+#endif
+
+}  // namespace electron
+
+#endif  // SHELL_COMMON_LANGUAGE_UTIL_H_

shell/common/language_util_linux.cc

@@ -0,0 +1,17 @@
+// Copyright (c) 2020 GitHub, Inc.
+// Use of this source code is governed by the MIT license that can be
+// found in the LICENSE file.
+
+#include "shell/common/language_util.h"
+
+#include "ui/base/l10n/l10n_util.h"
+
+namespace electron {
+
+std::vector<std::string> GetPreferredLanguages() {
+  // Return empty as there's no API to use. You may be able to use
+  // GetApplicationLocale() of a browser process.
+  return std::vector<std::string>{};
+}
+
+}  // namespace electron

shell/common/language_util_mac.mm

@@ -0,0 +1,25 @@
+// Copyright (c) 2020 GitHub, Inc.
+// Use of this source code is governed by the MIT license that can be
+// found in the LICENSE file.
+
+#include "shell/common/language_util.h"
+
+#import <Cocoa/Cocoa.h>
+#include <string>
+#include <vector>
+
+#include "base/strings/sys_string_conversions.h"
+
+namespace electron {
+
+std::vector<std::string> GetPreferredLanguages() {
+  __block std::vector<std::string> languages;
+  [[NSLocale preferredLanguages]
+      enumerateObjectsUsingBlock:^(NSString* language, NSUInteger i,
+                                   BOOL* stop) {
+        languages.push_back(base::SysNSStringToUTF8(language));
+      }];
+  return languages;
+}
+
+}  // namespace electron

shell/common/language_util_win.cc

@@ -0,0 +1,76 @@
+// Copyright (c) 2020 GitHub, Inc.
+// Use of this source code is governed by the MIT license that can be
+// found in the LICENSE file.
+
+#include "shell/common/language_util.h"
+
+#include <roapi.h>
+#include <windows.system.userprofile.h>
+#include <wrl.h>
+
+#include "base/strings/sys_string_conversions.h"
+#include "base/win/core_winrt_util.h"
+#include "base/win/i18n.h"
+#include "base/win/win_util.h"
+#include "base/win/windows_version.h"
+
+namespace electron {
+
+std::vector<std::string> GetPreferredLanguages() {
+  std::vector<base::string16> languages16;
+
+  // Attempt to use API available on Windows 10 or later, which
+  // returns the full list of language preferences.
+  if (!GetPreferredLanguagesUsingGlobalization(&languages16)) {
+    base::win::i18n::GetThreadPreferredUILanguageList(&languages16);
+  }
+
+  std::vector<std::string> languages;
+  for (const auto& language : languages16) {
+    languages.push_back(base::SysWideToUTF8(language));
+  }
+  return languages;
+}
+
+bool GetPreferredLanguagesUsingGlobalization(
+    std::vector<base::string16>* languages) {
+  if (base::win::GetVersion() < base::win::Version::WIN10)
+    return false;
+  if (!base::win::ResolveCoreWinRTDelayload() ||
+      !base::win::ScopedHString::ResolveCoreWinRTStringDelayload())
+    return false;
+
+  base::win::ScopedHString guid = base::win::ScopedHString::Create(
+      RuntimeClass_Windows_System_UserProfile_GlobalizationPreferences);
+  Microsoft::WRL::ComPtr<
+      ABI::Windows::System::UserProfile::IGlobalizationPreferencesStatics>
+      prefs;
+
+  HRESULT hr =
+      base::win::RoGetActivationFactory(guid.get(), IID_PPV_ARGS(&prefs));
+  if (FAILED(hr))
+    return false;
+
+  ABI::Windows::Foundation::Collections::IVectorView<HSTRING>* langs;
+  hr = prefs->get_Languages(&langs);
+  if (FAILED(hr))
+    return false;
+
+  unsigned size;
+  hr = langs->get_Size(&size);
+  if (FAILED(hr))
+    return false;
+
+  for (unsigned i = 0; i < size; ++i) {
+    HSTRING hstr;
+    hr = langs->GetAt(i, &hstr);
+    if (SUCCEEDED(hr)) {
+      base::WStringPiece str = base::win::ScopedHString(hstr).Get();
+      languages->emplace_back(str.data(), str.size());
+    }
+  }
+
+  return true;
+}
+
+}  // namespace electron

spec-main/chromium-spec.ts

@@ -319,7 +319,8 @@ describe('chromium features', () => {
       const w = new BrowserWindow({ show: false });
       await w.loadURL('about:blank');
       const languages = await w.webContents.executeJavaScript('navigator.languages');
-      expect(languages).to.deep.equal([appLocale]);
+      expect(languages.length).to.be.greaterThan(0);
+      expect(languages).to.contain(appLocale);
     });
   });