I'm wondering if there is a way to intercept the sentence currently being said by a character. Something similar to ".Speaking" or ".Moving" but with the sentence instead.
If such a property doesn't exist, how would you do? In dialogs it would be a pain to replace each line of dialog with something like cCharacter.SayCustom();
There is no such property, and even if there was, it wouldn't help you.
You would have to call your custom speech anyway, because if you use standard speech command the standard speech will be run and drawn, and not your custom speech.
The only solution I could think of is to implement custom speech callbacks in the engine API, similar to custom dialog options. That would solve every single problem related to speech at once...
As for now... well, unless I miss some trick, there's no other way but to explicitly call custom function everywhere.