Content translation of paragraphs I'm trying to translate paragraphs in Drupal 8. According to this bug report, which is marked as fixed, it should work.
#2543258: Entity references of untranslatable fields are not displayed in the correct translation is supposed to be fixed as well. 

I don't know if this has anything to do with it. Right now, I'm stuck and I even don't know if this really should work or not.

I'm doing the following:


In hook_preprocess_page there is $vars["node"] (as usual available via argument $vars)
On this node (could in fact be any arbitrary Node object, I guess) I will call $node->getFields()
One of the fields is a pararaph node ("field_sidepane")
I call "$field->view()" on this field to render the whole field (i.e. everything that's in the sidepane) at once. view() doesn't seem to support a second argument for the langcode or anything.
The sidepane contains multiple paragraphs (Cardinality=-1). One of these paragraphs contains a field "field_body" of type "text_long".  
This field is marked as translatable (under the Paragraphs section of the config page). field_sidepane by itself (appearing under the Content section of the config page), however, is not marked as translatable.
Apart form the minor glitch, that these paragraphs are wrongly labeled as "All languages" (which I think is https://www.drupal.org/node/2463575) everything works great during edit-time. I can edit text separately for the different languages etc.
On the page, however, only the primary language is ever shown. 


I thought it would be straightforward but I turns out to be surprisingly difficult. In the class Drupal\Core\Entity\Entity\EntityViewDisplay I discovered the following section:

      // The language of the field values to display is already determined
      // in the incoming $entity. The formatter should build its output of
      // those values using:
      // - the entity language if the entity is translatable,
      // - the current "content language" otherwise.
      if ($entity instanceof TranslatableInterface &amp;&amp; $entity-&gt;isTranslatable()) {
        $view_langcode = $entity-&gt;language()-&gt;getId();
      }
      else {
        $view_langcode = NULL;
      }


I've found that if I set $view_langcode to NULL, it seems to work. Obviously, it gets the language from the main entity. But I don't know how I can change this in any way (either programmatically nor via the UI). Even if I explicitly use $node = $node-&gt;getTranslation("en"); and call getFields() on the result, it doesn't seem to work. I could find no way whatsoever to render the field in the translated language.
Yes, that API doesn't support passing in the language.

I would recommend you use a view mode for what you are doing. You can click that together in the UI, configure the fields you want to see there and then just call $node->view('your_view_mode'). That should just work.

You could also use the Entity View block provided by ctools module, then you can place your sidebar as a block in a region and don't need any custom code at all.