I don't think you will face a case where you don't speak Chinese, but your Chrome Browser is set to Chinese, so Busy.org will display in Chinese. Unless you're using Busy directly in China, on a internet cafe.

I disagree. I live near Benidorm, you should see all the English in Internet cafes, trying to print their boarding passes. These pc's are normally set so Spanish, you can see people struggle to find the basic information.
While I agree browser detection is a better solution than geolocation, I still feel that besides the detection, language flags are very user friendly. A lot more than going to settings to change the language. Especially since that setting is "hidden" in the menu, I just found it for the first time because of this post ;-)