When using VS Code in remote mode with a non-English UI language, translations for built-in extensions (like Git source control) were missing and remained in English, while the rest of the UI was properly localized.

Root Cause

The issue had two main components:

1. Missing NLS keys in remote builds: The nls.keys.json file wasn't included in the remote server build, preventing proper NLS (National Language Support) resolution for built-in extensions.

2. UI language not propagated to backend: When scanning built-in extensions on the remote server, the current UI language wasn't being passed from the client, so the server couldn't load the appropriate translations.

Changes

1. Include NLS keys in remote server build

• build/gulpfile.reh.js: Added 'out-build/nls.keys.json' to serverResourceIncludes to ensure NLS keys are available in remote builds

2. Fix NLS resolution logic

• src/vs/base/node/nls.ts: Fixed the existence check to look for the actual language pack messages file instead of the cache directory, and reorganized Promise.all to avoid empty folder creation when keys file is missing

3. Propagate UI language through extension management chain

• src/vs/platform/extensionManagement/common/extensionManagement.ts: Added optional language parameter to getInstalled method signature
• src/vs/platform/extensionManagement/common/extensionManagementIpc.ts: Import platform language constant and pass it through IPC calls
• src/vs/platform/extensionManagement/node/extensionManagementService.ts: Updated getInstalled and scanExtensions to accept and use the language parameter

The language now flows: Client → IPC → ExtensionManagementService → ExtensionsScanner → ExtensionsScannerService.scanAllExtensions → scanDefaultSystemExtensions(language)

Testing

All changes maintain backward compatibility with optional parameters and minimal modifications to existing interfaces.

Fixes #250579.

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