I read your post on Multilingual plugins (https://metabox.io/best-wordpress-multilingual-plugins-reviews) with interest as it is something that I have been considering for a while.
Too often it seems that WordPress developers turn to complex or bloated plugins to provide functionality that can be better achieved using a multi-purpose framework or toolkit.
It would seem to me that the Metabox framework can do language translations without any additional plugins. Here are my basic thoughts on how it could be achieved:
1) Create TAXONOMIES for all supported LANGUAGES (approximately 100+)
2) Create the BASE post and assign the post's LANGUAGE to the relevant language TAXONOMY
3) Create TRANSLATED post(s) and relate them to the BASE post using MB Relationships
4) Create a URL structure like example.com/LANGUAGE/BASE or example.com/LANGUAGE/TRANSLATED
The flexible, extensible nature of Metabox could enable separate tables per LANGUAGE using MB Custom Table which (if properly indexed) would drastically speed free-text searching per LANGUAGE.
Clearly the above is highly simplified, but conceptually could be integrated anywhere (BBPress, REST, etc) using a variant of the method outlined in https://support.metabox.io/topic/custom-forum-posts
What are your thoughts?