This is the third beta release of the Search API Multilingual Solr Search. The minimum “officially supported” Solr version is still 4.5.1. The automated tests cover Solr versions up to Solr 6.4.2. For Solr 6.5.0 there’s a known issue in solarium.
This release only works in combination with search_api_solr 8.x-1.0-rc3.
If you encounter any strange issues, the first thing you should do is to create Solr config files and afterwards delete all the data from the index and start a re-indexing process!
There’s a video that demonstrates the creation of config files.