Customize the toArray method

In many cases, the toArray() method on Model the class is called under the hood to serialize your model.

To customize for all your models what should get returned for the translatable attributes you could wrap theSpatie\Translatable\HasTranslations trait into a custom trait and overrides the toArray() method.

namespace App\Traits;
use Spatie\Translatable\HasTranslations as BaseHasTranslations;

trait HasTranslations
{
    use BaseHasTranslations;

    public function toArray()
    {
        $attributes = $this->attributesToArray(); // attributes selected by the query
        // remove attributes if they are not selected
        $translatables = array_filter($this->getTranslatableAttributes(), function ($key) use ($attributes) {
            return array_key_exists($key, $attributes);
        });
        foreach ($translatables as $field) {
            $attributes[$field] = $this->getTranslation($field, \App::getLocale());
        }
        return array_merge($attributes, $this->relationsToArray());
    }
}