feat: add app.getSystemLocale() method

docs/api/app.md

@@ -723,6 +723,13 @@ Returns `string` - User operating system's locale two-letter [ISO 3166](https://
 
 **Note:** When unable to detect locale country code, it returns empty string.
 
+### `app.getSystemLocale()`
+
+Returns `string` - The current system locale, fetched using Chromium's `l10n_util` library.
+Possible return values are documented [here](https://source.chromium.org/chromium/chromium/src/+/main:ui/base/l10n/l10n_util.cc).
+
+**Note:** On Windows, you have to call it after the `ready` events gets emitted.
+
 ### `app.addRecentDocument(path)` _macOS_ _Windows_
 
 * `path` string

shell/browser/api/electron_api_app.cc

@@ -47,6 +47,7 @@
 #include "shell/browser/api/electron_api_session.h"
 #include "shell/browser/api/electron_api_web_contents.h"
 #include "shell/browser/api/gpuinfo_manager.h"
+#include "shell/browser/browser_process_impl.h"
 #include "shell/browser/electron_browser_context.h"
 #include "shell/browser/electron_browser_main_parts.h"
 #include "shell/browser/javascript_environment.h"
@@ -1039,6 +1040,10 @@ std::string App::GetLocale() {
   return g_browser_process->GetApplicationLocale();
 }
 
+std::string App::GetSystemLocale() {
+  return static_cast<BrowserProcessImpl*>(g_browser_process)->GetSystemLocale();
+}
+
 std::string App::GetLocaleCountryCode() {
   std::string region;
 #if BUILDFLAG(IS_WIN)
@@ -1785,6 +1790,7 @@ gin::ObjectTemplateBuilder App::GetObjectTemplateBuilder(v8::Isolate* isolate) {
       .SetMethod("setAppLogsPath", &App::SetAppLogsPath)
       .SetMethod("setDesktopName", &App::SetDesktopName)
       .SetMethod("getLocale", &App::GetLocale)
+      .SetMethod("getSystemLocale", &App::GetSystemLocale)
       .SetMethod("getLocaleCountryCode", &App::GetLocaleCountryCode)
 #if BUILDFLAG(USE_NSS_CERTS)
       .SetMethod("importCertificate", &App::ImportCertificate)

shell/browser/api/electron_api_app.h

@@ -191,6 +191,7 @@ class App : public ElectronBrowserClient::Delegate,
   void SetDesktopName(const std::string& desktop_name);
   std::string GetLocale();
   std::string GetLocaleCountryCode();
+  std::string GetSystemLocale();
   void OnSecondInstance(const base::CommandLine& cmd,
                         const base::FilePath& cwd,
                         const std::vector<const uint8_t> additional_data);

shell/browser/browser_process_impl.cc

@@ -297,10 +297,18 @@ void BrowserProcessImpl::SetApplicationLocale(const std::string& locale) {
   locale_ = locale;
 }
 
+void BrowserProcessImpl::SetSystemLocale(const std::string& locale) {
+  system_locale_ = locale;
+}
+
 const std::string& BrowserProcessImpl::GetApplicationLocale() {
   return locale_;
 }
 
+const std::string& BrowserProcessImpl::GetSystemLocale() {
+  return system_locale_;
+}
+
 printing::PrintJobManager* BrowserProcessImpl::print_job_manager() {
 #if BUILDFLAG(ENABLE_PRINTING)
   if (!print_job_manager_)

shell/browser/browser_process_impl.h

@@ -100,7 +100,9 @@ class BrowserProcessImpl : public BrowserProcess {
   void StartAutoupdateTimer() override {}
 #endif
   void SetApplicationLocale(const std::string& locale) override;
+  void SetSystemLocale(const std::string& locale);
   const std::string& GetApplicationLocale() override;
+  const std::string& GetSystemLocale();
   printing::PrintJobManager* print_job_manager() override;
   StartupData* startup_data() override;
 
@@ -110,6 +112,7 @@ class BrowserProcessImpl : public BrowserProcess {
 #endif
   std::unique_ptr<PrefService> local_state_;
   std::string locale_;
+  std::string system_locale_;
 };
 
 #endif  // ELECTRON_SHELL_BROWSER_BROWSER_PROCESS_IMPL_H_

shell/browser/electron_browser_main_parts.cc

@@ -320,7 +320,11 @@ int ElectronBrowserMainParts::PreCreateThreads() {
   }
 #endif
 
-  // Initialize the app locale.
+  // Fetch the system locale for Electron.
+  std::string system_locale = l10n_util::GetApplicationLocale("", false);
+  fake_browser_process_->SetSystemLocale(system_locale);
+
+  // Initialize the app locale for Electron and Chromium.
   std::string app_locale = l10n_util::GetApplicationLocale(loaded_locale);
   ElectronBrowserClient::SetApplicationLocale(app_locale);
   fake_browser_process_->SetApplicationLocale(app_locale);

spec/api-app-spec.ts

@@ -118,6 +118,12 @@ describe('app module', () => {
     });
   });
 
+  describe('app.getSystemLocale()', () => {
+    it('should not be empty', () => {
+      expect(app.getSystemLocale()).to.not.equal('');
+    });
+  });
+
   describe('app.getLocaleCountryCode()', () => {
     it('should be empty or have length of two', () => {
       const localeCountryCode = app.getLocaleCountryCode();

spec/chromium-spec.ts

@@ -374,6 +374,7 @@ describe('command line switches', () => {
   });
   describe('--lang switch', () => {
     const currentLocale = app.getLocale();
+    const currentSystemLocale = app.getSystemLocale();
     const testLocale = async (locale: string, result: string, printEnv: boolean = false) => {
       const appPath = path.join(fixturesPath, 'api', 'locale-check');
       const args = [appPath, `--set-lang=${locale}`];
@@ -394,6 +395,9 @@ describe('command line switches', () => {
 
       output = output.replace(/(\r\n|\n|\r)/gm, '');
       expect(output).to.equal(result);
+
+      const systemLocale = app.getSystemLocale();
+      expect(currentSystemLocale).to.equal(systemLocale);
     };
 
     it('should set the locale', async () => testLocale('fr', 'fr'));