Subscription form should work with Multilingual Taxonomy module

While working on #329778: Subscription form fails with multiple languages I noticed that the terms on the newsletter subscription form (newsletter/subscriptions) are not translated according to the Multilingual Taxonomy settings. With the attached patch the form will show translated newsletter terms (with 'Localize terms' setting) or only the newsletter term(s) matching the current language (with 'Per language terms' setting).

Patch committed.