"DefaultKeyBinding" Hex code for ML's "⌘ ⌘" Start Dictation command?
Changing the actions of double-presses of modifier keys is probably impossible. There isn't even a code point for the fn key in CORPCHAR.TXT.

But if you're looking to add a different shortcut for toggling speech, you should be looking for method names instead of shortcut strings.

I tried using strings to find method names for starting dictation. startDictation: and startSpeechCaptureForDictation: seemed promising, but neither worked in DefaultKeyBinding.dict.

Even if you were able to change the shortcut in DefaultKeyBinding.dict, it wouldn't work in applications that don't support the customizable keybindings.

What's wrong with just changing it in System Preferences?



If you want to use a shortcut that isn't allowed, you might be able to change CustomizedDictationHotKey in ~/Library/Preferences/com.apple.speech.recognition.AppleSpeechRecognition.prefs.plist.