Steps to reproduce:
1. Prepare a clean installation of Ibexa DXP and configure Solr to be your search engine.
2. Add a new folder "Test".
3. Add a new language e.g. pl-PL.
4. Create a new polish translation for "Test" folder.
5. Run php bin/console ibexa:reindex command.
6. Go to search and type "Test" using the default, eng-GB language filter.
7. Observe only one result.
8. Select Polish as the language for filtering.

Result:
You can see two results instead of one.

Note:
Legacy Search Engine produces proper results.