How can I determine a store owner's preferred language using REST API?

[DapTa]

Hi,

I am developing a Shopify app and would like to send emails to the store owner as notifications when certain events occur in my app, such as when they receive new reviews.

I need to determine the preferred language that the store owner uses so that I can customize the content of the email accordingly.

How can I achieve this via REST API?

I have tried the method described here: https://community.shopify.com/c/shopify-apps/how-to-display-an-app-in-the-user-s-selected-admin-lang..., but it does not work. The primary_locale value remains unchanged even I I change the language, and I do not use app bridge.

The language I need to retrieve is the one shown in the picture.

Thank you in advance.