Helper for localized (contentful) Entry type

LocalizedEntry.ts

/*
 * https://github.com/contentful/contentful.js/blob/master/index.d.ts#L81
 */

type Entry<Fields> = {
  sys: {
    id: string
  }
  fields : Fields
}

type LocalizedFields<Fields, Locales extends keyof any>  = {
    [FieldName in keyof Fields]?: {
      [LocaleName in Locales]?: Fields[FieldName];
    }
}

type LocalizedEntry<EntryType, Locales extends keyof any>  = {
 [Key in keyof EntryType] : 
  Key extends 'fields' 
  ? LocalizedFields<EntryType[Key], Locales>
  : EntryType[Key]
}

type MyFields = {
  a: string
  b: number
}

type MyLocalizedEntry = LocalizedEntry<Entry<MyFields>, 'en-US' | 'de-DE'>;

const myEntry: Entry<MyFields> = {
  sys: {
    id: "dfsdf"
  },
  fields: {
    a: "hello",
    b: 1
  }
}

const localizedEntry: MyLocalizedEntry = {
  sys : {
    id: 'my-id'
  },
  fields: {
    a: {
      "de-DE": 'german translation',
      "en-US": 'englisch translation' 
    }
  }
}

https://www.typescriptlang.org/play?#code/PTAEAsBdIBwZwFwgOYEtLgK4CMB0BjAewFtgiA7SAU0oDNMAbMwymyeh3AKzmGwcLZgxAIZxqAJ2CpyAEyoAPXLNyQ4AYgAyADgCMAKEgBPGFVABRShKMAeAGKoqDWXAB8oALygA3vtCg4I0QfP39QVFkEAMgJGWRQgF9Q2kdnOFAohycXfSTDEzNNQnwRBlQALypZLLT7VJcAGlAikoYqdMVqOXSAayojQlpQEXIjd08QsNAAbRrZADkRYjMZUD6Bobm4AF0AfijfKf9pltKqReXw8mbis5390C3Z+ouqbYBuUP8kvONTG9aFSqlhithB1gAKgUmqc2h0FF0XGt+oNhqNxl5DtMANL9K7IjYWKxGKGmbYZUChXFGUCdGhIgDkKWycAZlP8uwBpSB1XqcBs4JJBRx-W2MNucNcoSigtJVBFRm2uX0+X+AFkjFsJodhlFxLFyPF-NgouRMMRsFQJMrVWYNbCeYKJg7KrJBQLiTYNVtXE0GTQALQAVQAymyAD6gBnyAMAEXMDNcn30FHEoGIRkFMs93r57kxoUCwR1-giUQARLJaHAq+XEg1knyDl9daBy+AnAJyw2pibQAZvjbU5B00YXcDiVF7RLHcTtYWghSS+FIlGMwGIgz642Wc2piI90dK1Q4+Zy1EGcgraJrjERnAGCJIKgWAye0fA6Hz1GaMgynB8HAUA73IB8nxfcg2RbJJBySIA