The main I2P client implementation uses Java. If for some reason you can't use Java on your device, there are alternative implementations developed by community members.
i2pd is a I2P client implementation in C++. As of early 2016, i2pd has become stable enough to be used in production, and since summer 2016 it fully implements all I2P APIs.
Kovri är aktiv i2pd-förgrening utvecklad för kryptovalutan Monero.