Add en as fallback osLocale (#175039)

src/main.js

@@ -103,10 +103,12 @@ let osLocale = undefined;
 // Ref https://github.com/microsoft/vscode/issues/159813
 // and https://github.com/electron/electron/pull/36035
 if ('getPreferredSystemLanguages' in app
-	&& typeof app.getPreferredSystemLanguages === 'function'
-	&& app.getPreferredSystemLanguages().length) {
+	&& typeof app.getPreferredSystemLanguages === 'function') {
 	// Use the most preferred OS language for language recommendation.
-	osLocale = app.getPreferredSystemLanguages()[0];
+	// The API might return an empty array on Linux, such as when
+	// the 'C' locale is the user's only configured locale.
+	// No matter the OS, if the array is empty, default back to 'en'.
+	osLocale = app.getPreferredSystemLanguages()?.[0] ?? 'en';
 	if (osLocale) {
 		osLocale = processZhLocale(osLocale.toLowerCase());
 	}

test/smoke/src/areas/workbench/localization.test.ts

@@ -8,9 +8,7 @@ import { installAllHandlers } from '../../utils';
 
 export function setup(logger: Logger) {
 
-	// BUG: app.getPreferredSystemLanguages() doesn't seem to return anything here on Linux: https://github.com/microsoft/vscode/blob/3ba29f37d6b9f3f2257b48f2b90f0699ea581be4/src/main.js#L100-L113
-	// but it should when we move to Electron 22 so we can re-enable this test then.
-	(process.platform === 'linux' ? describe.skip : describe)('Localization', () => {
+	describe('Localization', () => {
 		// Shared before/after handling
 		installAllHandlers(logger);