How can I assign downloads from the media via API ?

If the downloads have already been uploaded to the media in the Shopware Admin, then I can assign the downloads via API as follows:

{
  "id": "f947b036a41c4be38cdad7fddf13bd1d",

  "acrisDownloads": [
    {
      "mediaId": "11d0ac3beb2e4f738f72732739e108b0",
      "title": "Test file",
      "position": 0,
      "languages": [
        {
          "id": "2fbb5fe2e29a4d70aa5854ce7ce3e20b" 
        },
        {
          "id": "7a6b724e70614488bc10740313df0409" 
        }
      ]
    }
  ]
}