Is it possible to invoke live translations within the app? (without going into the Call System UI)
You can enable/disable translation using CXSetTranslatingCallAction, but that's really the only API control you have.
Is it possible to navigate users from app to Call System UI via an API? (and also invoking the new live translations directly)
This is something developers have occasionally suggested since we changed CallKit's original behavior* during iOS 10's original beta, however, it might be worth reconsidering API for this give the new APIs options like live translation. Please file a bug asking for this, then post the bug number back here.
*Ironically, when we originally introduced CallKit, call reporting automatically brought up the in call UI and we actually changed to the current behavior based on developer feedback during that beta.
Will Apple support more languages apart from the current ones? (Currently I see 4 supported languages)
That's a question about our future plans that I simply cannot answer.
__
Kevin Elliott
DTS Engineer, CoreOS/Hardware