STM8 version of LCD2USB (AVR) is available on github
It is a modification of a working STM8 VUSB library from STM8S-VUSB-KEYBOARD. The Russian comments are "google translated" to English.
I have done some additional changes in the USB stack for the Vendor Request packets needed by LCD2USB. I have changed the device library files to bare metal, refractor the code. etc. I have taken the packet processing core from AVR LCD2USB, but used my own code for the I/O.
A general purpose schematic and PCB for Eagle is available. The serial, I2C pins are broken out with spare footprints for a tiny crystal (available on aliexpress) and caps.
I am not sure if/how the buttons (S1 and S3) works with LCD Smarties. LCD2USB.dll doesn't seem to an entry for them.
LCD2USB works with LCD Smarties LCD2USB.dll plugin as a info display. It should work with lcdproc in Linux (not tested).