Neo4j itself is implemented in Java and Scala. You can use JVM languages to extend Neo4j (e.g. with procedures and functions) but also to build applications. There is also a dedicated #drivers-stacks:spring-data-neo4j-ogm category. Usually people would use the neo4j-java-driver or existing wrappers e.g. for Kotlin or Clojure.
If you run into a bug, rather than posting it here, please create a GitHub issue.