Updated: Comment #N
The new entity translation API allows to pass around an entity object for a given language with
That makes the $langcode arguments useless and confusing (which language should be used now?), so it should be removed.
Remove $langcode from all $entity_view(), view_multiple() and render controller methods. Make sure that the correct translation is passed in elsewhere.
Write the patch. Possibly handle configuration entities somehow.
User interface changes
Removal of the additional arguments. Different way to access the entity fields, which is in line with the ongoing EntityNG changes.