101Leafy researched the game with the Hilltop Works fan translation patch, English translation by Cargodin
Hall Key is item 53 of the game's item table, in the Items group. The script names it on disc 2.
Lines of the script that name it, each with a link to its place in the script.
You're... giving me this? I see. I'm sure you heard, but sorcery is currently banned within City limits. We felt a powerful miasma flood the City this morning, but we can't use sorcery against it due to the ban. But if you can help, maybe, you can check the Hall of Imperial Supremacy for us. Here's the key to get in.
…これ、くれるのか…そうか…今この城内では妖術が禁じられてる、それは知ってるな…今朝がたから急に、城内に強い邪気を感じるんだ。妖術が禁じられてるから俺たちにはどうしようもないが、あんた、俺たちのかわりに調べてみてくれないか。ほら、皇極殿の鍵だ、たぶんあそこだと思うんだ。
Hall Key acquired.
「皇極殿の鍵」を入手しました。
Item table: Dried Wugu Worm Hall Key Warding Charm
English translations by Cargodin for Hilltop Works Fan Translation Patch: https://www.patreon.com/hilltopworks/posts/kowloons-gate-160555525?collection=18503