Here is a patch that removes the language manager dependency (credits to @Rhezios https://www.drupal.org/u/rhezios → )
I've made a patch to fix the problem reported by #6, see https://www.drupal.org/project/search_api_solr/issues/3326515#comment-14... 🐛 "can not use FieldCache on multivalued field" error when using boost recent dates processor Fixed
This patch works in combination with https://www.drupal.org/project/search_api/issues/3340305#comment-14940876 🐛 Aggregated fields are always declared as multivalued / list causing problems with boosting in search_api_solr Fixed to ensure the field prefix for aggregated fields works correctly.
Some code cleanup and name changes in this patch