Having trouble with on demand builder and permalinks

[lexoyo]

Hello dear community

I need some paginated pages to be rendered on demand with custom permalinks.

The initial data I have is this:

[
  { "permalink": "/en/test1/", "lang": "en", "id": "test1-en" },
  { "permalink": "/fr/test1/", "lang": "fr", "id": "test1-fr" },
  { "permalink": "/en/test2/", "lang": "en", "id": "test2" }
]

The permalink should has to be /en/test1/ for the 1st element

I can't find a way to do that, despite changing the data structure as explained bellow

What I tried #1

In _data/d.json

{
  "/en/test1/": { "lang": "en", "id": "test1-en" },
  "/fr/test1/": { "lang": "fr", "id": "test1-fr" },
  "/en/test2/": { "lang": "en", "id": "test2" }
}

In page.md

---
pagination:
  data: d
  size: 1
  serverless: eleventy.serverless.path.key
permalink:
  possum: /test/:key/

---
{{ pagination.items | first | json }}

It gives me an error (json.filter is not a function) because / are not supported apparently - I could not find where is the matching made in the source code

What I tried #2

In _data/d.json

{
  "test1": { "lang": "en", "name": "test1" },
  "test1fr": { "lang": "fr", "id": "test1" },
  "test2": { "lang": "en", "id": "test2" }
}

In page.md

---
pagination:
  data: d
  size: 1
  serverless: eleventy.serverless.path.id
permalink:
  possum: /test/:lang/:id/

---
{{ pagination.items | first | json }}

This will not let me choose id and lang from inside the object, this will match both /en/test1/ and /fr/test1 to the same object with key test1 :(

What I tried #3

The only workaround I found is to use GET params in the URL to pass the ID and the language, so my urls are all messed up with GET for on-demand pages and a normal path for the other ones 😬

Any suggestions? I can change the data structure as it comes from directus.io headless CMS