I agree we need more clarification on what you are trying to do @onebitknightly before really answering.
If you are doing more true API try stuff then you should stick with the standards that most application and open source companies use which is JSON for data and Python for the rest of it.
Java is massively heavy on memory use as you scale so I wouldn’t recommend that. C+/#, etc are mostly used on Windows and not easily ported to Mac. Others have pro/cons and could start a religious debate from all of us IT people.
Personally, I would be asking the Boundless programmers which they recommend best interfaces with their World Builder and Application as a whole for API interaction.