Dictation regression in 1.141.0: on-device model ignores Spanish and leaks the <en-US> token (works in 1.140.0) #341152

Type: Bug

VS Code version

• Broken: 1.141.0 (commit 2a59476c9bfcb90b3ddc372c36762471b7dfad1c)
• Works: 1.140.0 (commit 07f806f999227108933c2e30515b26eecc1fda74)
• OS: Ubuntu (Linux x64)

Steps to reproduce

1. Set "agents.voice.language": "es".
2. Open Copilot Chat and use the built-in Dictation with the on-device backend (default). Model: nemotron-3.5-asr-streaming-0.6b.
3. Dictate a sentence in Spanish (optionally mixing in some English words/abbreviations).

Expected

The Spanish text is transcribed and inserted correctly into the chat input.

Actual (on 1.141.0)

• The audio is transcribed as if it were English, and the language tag token <en-US> is leaked into the inserted text.
• Sometimes nothing gets inserted into the input.
• Happens with the exact same settings that work perfectly on 1.140.0.

Evidence / root-cause analysis

• The only relevant change between the two versions in product.json is the dictation runtime:
  • 1.140.0: "dictationRuntime": { "version": "1.2.3", "urlTemplate": "https://main.vscode-cdn.net/dictation-runtime/foundry-local/1.2.3/{target}.tgz" }
  • 1.141.0: "dictationRuntime": { "version": "2.0.1", ... }
• Language resolution for the local backend is identical in both versions (_startLocalSession() -> ihn(configurationService.getValue("agents.voice.language"), navigator.language)). With "es", Eso("es") returns "es-US" (internal table cAr = { ..., es: "es-US", ... }; navigator.language is en-US).
• That value is passed to Foundry Local: session.settings.language = "es-US" (see out/vs/platform/localTranscription/node/localTranscriptionMain.js).
• The 2.0.1 runtime (libfoundry_local.so) only contains lowercase language strings - de-de, en-gb, en-us, es-es, es-us, fr-ca, fr-fr, it-it, pt-br, pt-pt - and includes this failure path:
  Failed to set Nemotron lang_id '{}' for '{}': {}
• Result: es-US is not applied, the model falls back to English, and it emits the <en-US> token (present in the model vocab at index 2948).

Workaround

Downgrade to 1.140.0 (which uses runtime 1.2.3) and hold it:

sudo dpkg -i code-1.140.0.deb
sudo apt-mark hold code

Dictation works again immediately.

Suggested fix

• Compare language codes case-insensitively when setting lang_id (es-US -> es-us), and/or make the 2.0.1 runtime accept the case produced by the workbench (Eso/Intl.getCanonicalLocales always outputs Title-Case regions).
• Consider exposing the Spanish-specific local model nemotron-speech-streaming-es-0.6b-ft (already in foundry.modelinfo.json) in the dictation.model picker.

Attachments

• Developer: Show Logs... (Window channel) captured while reproducing on 1.141.0.
• Screenshot of the inserted text containing <en-US>.

VS Code version: Code 1.140.0 (07f806f, 2026-09-30T10:38:38+02:00)
OS version: Linux x64 7.0.0-38-generic
Modes:

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