Translation is broken for languages with locale or dialect

Problem/Motivation

Language code can have two parts, like en-GB or zh-hans. We want to support this format

Steps to reproduce

1. Enable a language with dialect, e.g. zh-hans
2. Make translations for a node
3. Query the node with a specific translation, example query below

query MyQuery {
  entityQuery(
    entityType: NODE
    filter: {conditions: {field: "type", value: "article"}}
  ) {
    items {
      ... on NodeArticle {
        id
        translation(langcode: ZH_HANS) {
          label
        }
      }
    }
  }
}

Notice the language ENUM `ZH_HANS`, it was defined with the underscore. This underscore isn't converted back to hyphen when the server receives the query.

Therefore, you cannot get this specific translation

Proposed resolution

Correctly convert the language ENUM back to the code used by Drupal

Remaining tasks

Make a patch

User interface changes

None

API changes

None

Data model changes

None