How to model a json object with dynamic keys in typescript

Our backend is returning most string data as json object strings where each key represents a language code that may or may not exist on a particular database record. For example, it will come down as:

{
 "id": "4788fb8d-fb63-4189-a9e8-68624180852e",
 "description": "{"en":"description of co","es":"descripción de la co"}", "options": "[{}]"
}

Or:

{
    "id": "4788fb8d-fb63-4189-a9e8-68624180852e",
    "description": "{"en":"description of company"}",
    "options": [{"en":"english text"},{"en":"english text","es":"spanish text"},{"en":""}]
}
etc..

What is an appropriate way to represent this type across our whole web app so all our objects can be safely worked with? I’m sure this is probably a bit naive:

  interface StringType {
    en: string | undefined;
    es: string | undefined;
    de: string | undefined;

  }

interface Customer {
   id: string; 
   description: StringType;
   options: StringType[]; //
}

And how would I narrow the keys to only be our supported language codes, for example ‘en’ or ‘es’ or ‘de’ instead of any string?