Can confirm that it's Diplomatic Total which makes that the Interface disappears -which is normal as it has to be replaced with a civ's communication screen- when encountering a new civ or when that civ contacts you for deals or whatever.
Hitting a civ's icon top right of the screen (including one's own) has the same effect; the civ's communication/info screen doesn't show, leavingthe player with the game's overview with no means of advancing the game. Ambient sounds continue; dialogue is missing also.
Activating and using the console doesn't help.
Hitting "Escape" luckily shows the menu, so you can exit the game. Reloading a save brings back the interface, but the game is utterly unplayable like this with Diplomatic Total enabled...
Had 22 mods active. Deleted them all and tried the game by adding a mod one at a time. Diplomatic Total was the fourth added (after 8 Ages Of Pace; Better National Parks; Daughter Of Seth) and the one that screwed-up.
Is an update among the possibilities, please?