override product name/description per checkout session, and full translation with force_language in Checkout dialog

The setting force_language works well for most of the checkout. However, the order summary card still shows English texts, so we can't offer a checkout fully in the customer's language. We'd like to request two improvements.

1. Override the product name and description per checkout session

A product can only have one name and one description, maintained in the dashboard. We'd like to set both per cart item when creating a session, for example:


{
  "product_cart": [
    {
      "product_id": "pdt_...",
      "quantity": 1,
      "product_name": "Basic (monatlich)",
      "product_description": "Bis zu 20 Teilnehmer, unbegrenzte Speicherdauer, ..."
    }
  ],
  "customization": { "force_language": "de" }
}
Alternatively, translated product names and descriptions per language could be stored on the product and picked automatically according to force_language.

We tried product_description on a cart item with the current API. The request is accepted, but the checkout still shows the description from the dashboard. As far as we can see, the field currently only works for on-demand subscriptions (subscription_data.on_demand.product_description).

2. Translate the billing interval in the forced language

With force_language: "de", the price in the order summary still shows as "€10.00 / Month". "Month" seems to be the raw interval value (Day | Week | Month | Year), so it isn't translated. We'd expect "/ Monat" in German, and likewise for the other supported languages.

In the same test we also noticed that these stay in English:

the currency selector ("Pay in EUR");

The price is also formatted as "€10.00" instead of the German "10,00 €".

With these changes, the entire checkout card could be shown in the customer's language.