Wire the directive into Apollo server.

server.js

// Importing the directive
const intlDirective = require("./intlDirective");
const typeDefs = gql`
  directive @intl on FIELD_DEFINITION
  type Query {
// declaring we want to use the directive
    # Makring "greeting" field for internationalization.
    greeting: String @intl
    id: Int
  }
`;

// ....

const server = new ApolloServer({
  typeDefs,
  resolvers,
  context: async ({ req }) => {
    // .....
  },
  // Wire our directive into the config object.
  schemaDirectives: {
    intl: intlDirective,
  },
});