[{"locale":{"en":{"dashboard":{"DASHBOARD_TITLE":"Some title"}},"fr":{"dashboard":{"DASHBOARD_TITLE":"Some title french"}},"pr":{"dashboard":{"DASHBOARD_TITLE":"Some title portugues"}}}}]

db.collection.aggregate([{"$project":{"locale":{"$arrayToObject":{"$filter":{"input":{"$objectToArray":"$locale"},"as":"el","cond":{$eq:["$$el.k","en"]}}}}}}])