Shopify REST API: Send Invoice With A Specific Locale

In shopify, when you buy from a translated storefront, you automatically get the invoice in the correct language.

I want to achieve the same thing with the Shopify REST APIs. Unfortunately, the API documentation doesn't show anything to set the locale.

How can I specify a locale when sending an invoice with Shopify REST API?

After months of digging and no support feedback of any kind of Shopify devs, the answer at this date is now clear:

This is simply not possible

If you need this kind of feature you need to implement in your site email generations.