Laravel Dingo API is not returing UTF8 encoded characters - laravel

Question

I've just inherited a project in Laravel and it's using Dingo API.
The API is returning strings like Federaci\u00f3ninstead of Federación.
All strings are correctly UTF-8 encoded in the database, so the problem is in the server.
The controller is returning $this->response->paginator($articles, new ArticlesCollectionTransformer); and inside ArticlesCollectionTransformer I placed a var_dump for the strings I have issues with and they are correctly encoded there.
Where else should I look? What am I missing?
Controller:
public function index(Request $request)
{
$limit = (0 === (int)$request->limit || $request->limit > self::PER_PAGE) ? self::PER_PAGE : $request->limit;
$articles = Article::with('author', 'category')
->approved()
->orderBy('published_at', 'desc')
->orderBy('featured', 'desc')
->paginate($limit);
return $this->
response->
paginator($articles, new ArticlesCollectionTransformer)->
// also tried:
// withHeader('Content-type', 'application/json; charset=utf-8');
}
Transformer
class ArticlesCollectionTransformer extends TransformerAbstract
{
public function transform (Article $article)
{
// var_dump($article->title) ==> is correctly encoded
return [
'id' => (int) $article->id,
'category' => $article->category->name,
'author' => $article->author->name ?? ArticleAuthor::DEFAULT_AUTHOR_FOR_NEW_ARTICLES,
'display_order' => (int) $article->display_order,
'title' => $article->title,
'featured' => (bool) $article->featured,
'viewed_times' => (int) $article->viewed_times,
'last_update' => $article->updated_at->timestamp,
];
}
}
More info:
Laravel: 5.2.*
dingo/api: 1.0.x#dev