You can change the locale programmatically in an Espresso test too.

Here you can find a quick example I wrote.

The key part is to restart the Activity after you have set the new Locale.

Of course you can also set the flag of ActivityTestRule to manually re-launch the Activity so that you launch it after you set the new Locale.

Just ensure you have a new Activity after you change Locale.

Bear in mind that to change the locale taking into account all the deprecations and sdk versions is more complex than the code I wrote in my example. Read more here.