Does SAP NW AS Java support all the language on JVM(Kotlin, Scala, Jython..), or only Java? If not is there a way to use other languages for SAP other than ABAP and Java?
Yes. It depends on the SAP JVM version you have.
I believe that web based languages are available to use in specific contexts, but I believe they require ABAP or JAVA wrapper code.
Check this link out for more information.
https://blogs.sap.com/2011/12/07/sapjvm-overview/
Platform Runtime JDK
As Java 6.40 SAP JVM 4 (via switch)
As Java 7.00 SAP JVM 4 (via switch)
As Java 7.0 EHP3 SAP JVM 4
As Java 7.10 SAP JVM 5
As Java 7.20 SAP JVM 6
As Java 7.30 SAP JVM 6