All the good work to make sure that `getActivity()` actually returned
a proper context, obtaining a final reference to that known good activity
object, and then using that in the background thread is thrown away.
The reason was because the `translateCategories` method would go and
call `getActivity()` all over again. This changes the `translateCategories`
helper function so that it asks for a `Context`. This way, a known
good `Context` can be passed in, rather than having to perform a check
to see if `getActivity()` is good again.
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