Enable marketing email opt-in in more languages

[rfk]

Ref https://bugzilla.mozilla.org/show_bug.cgi?id=1179873

We can usefully enable this checkbox for the following languages, which have localized newsletter content: DE, ES, PT-BR, RU, ID, FR, HU, PL.

[shane-tomlinson]

@rfk - Ben Niolet mentions in the referenced bugzilla bug that we'd have to pass the user's language down to Basket. This bug is more than just enabling the opt-in for those locales. :/

[rfk]

Per #2452 (comment) the path forward seems to be to just pass on the raw Accept-Lanuage value and let basket figure out how to turn it into a lang. I'll follow up in the linked bugzilla bug.

[shane-tomlinson]

Possibly no work in the content server, dependent on the response to https://bugzilla.mozilla.org/show_bug.cgi?id=1179873#c3. mozilla/fxa-content-experiments#25 has been opened to enable more locales.

[rfk]

Looks like they're going to add the ability to send accept-language with the subscription request: https://bugzilla.mozilla.org/show_bug.cgi?id=1188047

We'll need to wait for the final shape of that API before we can move this forward, but I expect it to be a fairly minor change on our side (e.g. passing along literal accept-language header somehow)

[shane-tomlinson]

Looks like they're going to add the ability to send accept-language with the subscription request: https://bugzilla.mozilla.org/show_bug.cgi?id=1188047

So, we have to shuttle the accept-language with the subscribe request and the locale sent in the fxa-register call is ignored?

[rfk]

Not ignored, but may not be processed reliably by the time they need this information during the subscription process.

[shane-tomlinson]

Removing from train-43. Once the Basket portions are available, we can assign this to a train.

[rfk]

Basket component in review here: mozilla/basket#143

[rfk]

The modified subscription endpoint is now available in basket: https://bugzilla.mozilla.org/show_bug.cgi?id=1193364