Import channel search: language filtering requires re-thinking

Observed behavior

Filtering by language in import channel search isn't working as expected.

Expected behavior

Filtering by language should work as expected.

User-facing consequences

Wrong results when filtered by language.

Additional information

Presently, filtering by language in import from channel search uses contentcuration's model's language value. But we set language during publish on exported database. So, filtering by language is giving wrong results.

We need to handle this for both channel types -- public, and private.

Steps to reproduce the issue

1. Create a channel with a specific language.
2. Add a resource without setting its language explicitly.
3. Publish that channel.
4. Create another channel.
5. Go to import channel search.
6. Select My channels from Channels dropdown.
7. Now, enter a search term that displays that resource.
8. In the results page, in Language dropdown, select the published channel language.
9. You will see zero results.

Usage Details

• OS: Ubuntu 22.04
• Browser: Chrome
• URL: Latest unstable

Start at the import channel search language filter and trace how language is read for published resources. Compare the model language with the language set during publishing for both public and private channels, then reproduce the listed steps and confirm that the expected channel language returns the resource.