For our schema, we store multi language version of our fields as an object, e.g.

{ title: {type: Object} }

And below is an example of the data we save

{
  title: {
    en: "abc",
    jp: "ひらがな"
  }
}

However, we will add language from time to time and do not want to edit the schema everytime,

How should we do indexing for the title field in each language properly so it can be searched easily?

We use Mongoose and Node.js