What is your system level language? Normally it's not possible for an iOS app to run in a different one, unless you see a language item in Settings > GMail, or the app has no localization for the system level language.
– Tom GeweckeJun 30 '19 at 09:17
My system-level language is Chinese. And I can't find a language item in Settings > GMail. What I need is to switch to English, which is definitely existed in the app, without switching my system-level language to English.
– AGamePlayerJul 01 '19 at 00:02