How handle i18n(with fallback) on MongoDB when translation is in another Collection?

Given these excerpt collections:

Translation Collection

[
    {
      "_id": "id01_name",
      "text": "Item's Name"
    },
    {
      "_id": "id01_desc",
      "text": "Item's lore description"
    },
    {
      "_id": "sk_id",
      "text": "Item's skill description"
    },

  ]

Item Collection

[
    {
      "_id": "id01",
      "name": "id01_name",
      "lore_description": "id01_desc",
      "skill": {
        "description": "sk_id01",
      }
    }
  ]

---

Question:

Using only mongodb driver (NO Mongo ODM, like mongoose, iridium, etc), what is the best approach for (i18n) Internationalization (with fallback) on MongoDB when translation is in another Collection?

---

MongoDB's aggregate Approach

Currently, I'm using aggregate with $lookup to do these kind of queries.

db.artifact.aggregate([
  { 
    $lookup: { // get the name's data from the english translation
      from: "text_en", 
      localField: "name",
      foreignField: "_id",
      as: "name"
    },

  },
  {
    $unwind: "$name" //unwind because the lookup made name become an array with _id and text
  },
  {
    $addFields: {
      name: "$name.text" //rewrite name (currently an obj) into the translation string
    }
  },

(...etc)

Problem is, I need these 3 steps on every single key I need to translate. On a big document, looks a bit too much, and every $lookup feels like the response time increases bit by bit.

This also doesn't have fallback cases, in case key is not available in said language, e.g., try $lookup on id01_name in the Spanish collection but the collection doesn't have it, so a fallback would be get from English collection.

Here a working example of the example above: https://mongoplayground.net/p/umuPQYriFRe

---

Manual aggregation Approach

I also thought in doing in phases, that is,

• item.find() to get item data;
• translation_english.find({ $in: [ (...listofkeys) ]}) to get all necessary english keys
• translation_{otherlang}.find({ $in: [ (...listofkeys) ]}) to get all necessary other language keys
• manually transform the two translation arrays into two objects (with cursor.forEach()), merge with Object.assign({},eng,otherlang)
• handpicking each key and assigning to the item object

This method covers the fallback, but it's bloated/very verbose.

---

On a test with both attempts, lookup took 310ms and the manual took 500ms to complete, that for one lookup. But manual has fallback (aka queries 3 collections; item, lang_en, lang_{foreign}). If language key does not exist in foreign, it'll pick the en (it's assumed eng will never miss a key). While lookup fails to return a document when the lookup on foreign lang fails.

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