When is the customer.locale value updated in Shopify?

[RomanoC]

Hello,

I wonder when does the customer.locale value is updated?

There are 2 articles on the topic on the Shopify Community and yet, neither of them is answered precisely.
https://community.shopify.com/c/Shopify-APIs-SDKs/Checkout-Customer-Locale/m-p/448845
https://community.shopify.com/c/Technical-Q-A/Change-Customer-Locale/m-p/1043096#M45357

I know (I have made the test) that once a new customer arrives on the website the value is populated straight away. If they change the language (I'm using the app LangShop) and start the checkout, the value is updated. Let's say that the same customer is starting to browse in a new language (Maybe that person is bilingual and somehow, he rather browsing in the new language). At what point the value for this customer will be updated?
Once he changes the language?
Once he interacts more with the website (Starting checkout)?
Once he makes an order?

Thank you for the help!

Romano