Nothing, they just have yet to add "large" as a translation alongside "big". Report it.
Via the "Report a Problem" button (next to the "Discuss sentence" which leads here), or by tapping on the flag icon on mobile phones.
In English it should be "big, beautiful city..." Even though the order of adjectives says opinion should be first, in this case 'big, beautiful' makes more sense and should at least be accepted as an answer... Yes, I've reported it.