function makeVariant(variantLanguage, audioLanguage, videoLanguage) {
      // This returns a subset of the fields that would be in a variant.
      // However, we know that we are only operating on the language fields
      // so we are going to be lazy and only set them.
      const sparse = {
        language: variantLanguage,
        audio: {
          language: audioLanguage,
        },
        video: {
          language: videoLanguage,
        },
      };

      // Cast the sparse object to a variant to make closure happy.
      return /** @type {shaka.extern.Variant} */ (sparse);
    }
@param {string} variantLanguage
@param {string} audioLanguage
@param {string} videoLanguage
@return {shaka.extern.Variant}