This isn't the final solution and I assure you a real solution is being worked on, but here's something that I got working. It's a third-party application, but it's a useful tool for anyone fluent in more than one language on their Mac.
Using this launcher, it will force-launch Puzzle Agent to English without changing your system settings. I already confirmed this on my Mac after switching to German as a system language. Don't worry about the launcher saying there's only English, it will launch correctly.
I want to stress that this isn't the final solution and that a real fix is being worked on. Relying on a different application is not a solution. I know this will come back with some flames about using a third party application. Just know that this isn't considered the
fix, but this will work for the time being.