Design: Show localized activities

[gideonthomas]

We need design guidance for how we will show activities that have been localized into different languages.

Here's an example of what we do with club guides: https://learning.mozilla.org/en-US/clubs/running (where we show translated guides below the English one).

/cc @hannahkane and @xmatthewx

[hannahkane]

This ticket should be done with reference to the new design being worked on in #2283

[hannahkane]

We also need to think about the logic here. For example, we should prioritize activities that are in the user's locale (as determined by locale detection rules documented elsewhere). This ticket could be about answering questions like:

• Do we show that a particular activity has a counterpart in another language or locale? If so, under what circumstances? What is the UX/UI?
• Do we show activities that aren't in the user's locale/language? Under what circumstances? What is the UX/UI?
• What control do we give the user over what they see when it comes to content in multiple languages?

[hannahkane]

cc @flukeout @taisdesouzalessa - probably good for the two of you to team up on this. @flukeout - not sure if you want to be considering localization as you work on #2283, or leave it for a later task.