It is possible to have a speech line display on-screen indefinitely by use of the [hold] token - see the "Text tokens" chapter of the Manual.
However, as AC still places each line in its own menu, I suspect that something like this is best achieved with a custom-made UI system. AC's speech/translation/audio systems can still be used, I'm only talking about the way in which dialogue itself is displayed on screen.
You should look into using the OnStartSpeech custom event, a tutorial for which can be found here. This essentially allows you to run your own code whenever a line of dialogue begins, allowing you to forego AC's own dialogue displaying functionality in favour of your own one, which instead adds each line to the same UI.
Comments
It is possible to have a speech line display on-screen indefinitely by use of the [hold] token - see the "Text tokens" chapter of the Manual.
However, as AC still places each line in its own menu, I suspect that something like this is best achieved with a custom-made UI system. AC's speech/translation/audio systems can still be used, I'm only talking about the way in which dialogue itself is displayed on screen.
You should look into using the OnStartSpeech custom event, a tutorial for which can be found here. This essentially allows you to run your own code whenever a line of dialogue begins, allowing you to forego AC's own dialogue displaying functionality in favour of your own one, which instead adds each line to the same UI.