Importing localized upload fields via Local API in one create call

[Dimbreath]

I'm working on a project in which I enabled the localization feature Payload provides, and it seems to work just fine on text fields. I can set the locale to * when calling payload.create and then I can set all the languages at once by providing an object like:

{"en": "a", "es": "b"}

However this same logic seems to fail when it comes to upload type fields, complaining that the field is invalid. From reading the documentation and experimenting via the UI it's clearly supported to localize upload fields so I'm wondering if it uses another way, if it's a bug or if it's simply not supported? I assume it may have to do with the fact that it's a relationship field.