If I understand your question correctly you want to rename one of the result columns to something else?
In SQL you can do that quite easily
SELECT column as column_alias
FROM table:
Not an master of Eloquent but there should be something similar to give the column an alias.
On You Controller
->comments()
->with('translationCHN');
->get();
On You Model
public function translationCHN()
{
return $this->belongsTo('App\Models\Comments','word_id','word_id')
->where('comment.sentence_id',$this->sentence_id);
}