We have this:

ATM a campaign admin can add a default caption for a campaign like this:

{
    "enabled": true,
    "wikibase": {
        "enabled": true,
        "captions": true
    },
    "defaults": {
        "caption": "SOME CAPTION"
    }
}

... but if they want to set the caption's language they need to use captionlang= in the url

We want this:

A campaign admin to be able to set language/caption pairs in the caption config, like this

{
    "enabled": true,
    "wikibase": {
        "enabled": true,
        "captions": true
    },
    "defaults": {
        "captions": [
            { "language": "en", "text": "SOME CAPTION" },
            { "language": "ga", "text": "CAPTION ÉIGIN" }
        ]
    }
}

During development, please test the following:

• Test this feature as a campaign admin AND as a uploader
• Test uploading multiple images, and make sure the defaults appear for them all