Localization for the in-app payments UI is different than the rest of the site because it starts with a JavaScript include and then will need to check accept headers and/or cookies to decide what localization to use. We currently have developers include this: https://marketplace.mozilla.org/en-US/inapp-pay/mozmarket.js but we want them to include this: https://marketplace.mozilla.org/inapp-pay/mozmarket.js yet still decide which localization to display. BrowserID recently added localization so we can learn from them.

looks like browser ID just checks the accept header. https://github.com/mozilla/i18n-abide

The JS file moved here: https://marketplace.mozilla.org/mozmarket.js https://github.com/mozilla/zamboni/commit/9d5deb6cf72889f6db7f6a1fa72bb9d3949a56a1 As for localization, the iframe opens up to the mkt site which does an accept header check. I just verified that this header is indeed recognized by the iframe so localization will work as expected.