Before Jon kills her, Daenerys gives a big, rousing speech to her troops about how thankful she is they helped her take King's Landing, and how she doesn't plan on them stopping anytime soon. No, the Dragon Queen has her sights set on breaking the chains of the rest of the Westeros, imploring her army to "break the wheel" with her. This, to Tyrion and anyone else with a rational brain, is basically code for "I now know I'm powerful enough to take over the world by any means necessary, so what are we waiting for, y'all?! Let's get to murdering!" (Or something along those lines.)
But, wait a second — how does Tyrion know that's what Daenerys says when she's making her speech on that staircase? He's standing right next to her, sure, but she's not speaking English. Instead, she addresses her troops in the Valyrian and Dothraki tongues. The last time we checked, Tyrion doesn't speak either of those languages even close to fluently, if at all. (Remember the trouble he had conversing with the Unsullied guard outside of Jaime's tent?) Missandei obviously isn't around to translate anymore. So, I guess we can just add this to the never-ending list of Game of Thrones season eight plot holes.