Testing In-App purchases for multilanguage

I have included various localized descriptions in iTunesConnect (English, French, Chinese) for an in-app product. I am displaying the localizedTitle and localizedDescription properties after fetching them from apple's server using an SKProductsRequest.

My understanding from the docs and other threads is that if I change the test phone to the relevant language it will display the correct language. However in testing with my phone in French or Chinese the product descriptions are still in the original English.

I am not logged on with any iTunes account during the testing (Settings=>Store=>Signout).

Can anyone provide any hints how to test the IAP multilingual functionality?

Can I test in-app purchase in TestFlight?

Your TestFlight user is a legitimate App Store user, but doing in-app purchases made with beta builds are free within the context of the beta version. You can enable up to 25 users per app from your iTunes Connect team to be internal testers and up to 2000 users to be external testers per app.

I believe the localization that the store returns for the product description is based on the assigned iTunes store of the test user you are using. The device's language setting only pertains to the resources loaded locally.