Fact · Dictation in your apps
When a page sets processLocally to true but the correct on-device language pack is not installed, start() fails with a language-not-supported error.
Checked against its source on October 17, 2026
In the source's own words
“If you run the start() method after specifying processLocally = true but the correct language pack isn't installed, the function call will fail with a language-not-supported error.”
SpeechRecognition: available() static method, MDN Web Docs (Mozilla), 2026, Examples: Checking on-device availability and installing language packs.
Open the original- What it measures
- MDN's worked example for the Web Speech API's on-device mode. It applies to a web page that asks for on-device recognition, not to a dictation tool that uses the browser's default server path.
- What it does not show
- The page is marked experimental. The error name is the one MDN documents, and browsers may report it differently in future versions.