You can implement strategies and make full use of the AlgoTrader services with Python 2 and 3 - see http://doc.algotrader.com/html_single/index.html#Python_Strategy_Development
AlgoTrader also provides a public REST and websocket API that can be used from any programming language to receive market data and send orders in live trading.
It is not currently possible to run a back test from languages other than Java and Python.
It is however possible to provide signals from external systems into AlgoTrader (both in live trading and backtesting) that are then acted upon by trading strategies written in Java running inside AlgoTrader.
So for example, it is possible to calculate target positions in another program and then have the Java based trading strategy running inside AlgoTrader execute orders.
Also it is possible to call mathematical operations (e.g. related to artificial intelligence and machine learning) written in other languages both during live trading and back testing.
To make use of the ready-made business services that AlgoTrader offers, the actual strategies need to be written in Java.