Add images to the gallery attribute

mutation {
  productAddAttributeValueTranslationsGallery(
    input: {
      sku: "1"
      attributeCode: "gallery"
      translations: [
        { language: "pl_PL", value: ["1.jpg", "2.jpg", "3.jpg"] }
      ]
    }
  ) {
    __typename
  }
}

Attribute Gallery and Product identified with SKU must already exist.

value: is the path to an image, you can get it with query "multimediaStream"