Sauce Labs provides a way for you to choose the language for a specific real device project.
This setting provides two different experiences on iOS and Android.
Android
On Android the language set in the Device Settings menu will change the language on the entire device.
This means that not only the application will change language, but also the Operating System.
iOS
On iOS, the application locale is changed, and not the system locale.
This means that the OS's Language & Region settings will still be set to their default (English - UK)