I wrote a FTS14 to MQTT bridge a couple years ago. And it works fine so far. It is running on a Raspi 3, the USB attached to an Eltako FGW14.
But the code is quite old (Python 2.7 and twisted 14) and is currently running with an OpenHAB installation 1.6 (really old). If you still need the code, drop me PM and I can sent you an export.