Multilingual content is not taken into account when indexing

Problem/Motivation

If you have multilingual nodes, the module does not take into account which translation we are currently editing / previewing.

For example, if you have a node with 3 translations, it loops through all 3 translations, and indexes them all to the same content index, under same node id. Thus the last indexed content is not necessarily the same one we were editing, this seems rather random.

Steps to reproduce

- Create node with multiple translations
- Try previewing node translations one by one

Proposed resolution

Attached is a patch that we had success using. We make it so that the active langcode from the node is suffixed to the index, thus saving and serving the right content.

Remaining tasks

User interface changes

API changes

Data model changes