This is a very minor firmware update (unless you are using the simplified Chinese language).
From Canon USA:
Canon has released a firmware update for the EOS C300/C300 PL Cinema EOS Cameras. Affected Products
EOS C300 Cinema EOS Camera
EOS C300 PL Cinema EOS Camera Firmware
Firmware Version 18.104.22.168.00 incorporates the following features:
1. Genlock synchronization can now be used to synchronize the camera’s 24.00P, 24.00PsF, 23.98P, and 23.98PsF input signals.
2. Adds the Korean language to the camera’s menu.
3. Minor corrections to simplified Chinese language menus. Note:
Firmware version 22.214.171.124.00 incorporates item 1 and 2 above.
The new firmware (126.96.36.199.00) for the EOS C300 camera can be downloaded by clicking here
For the EOS C300PL camera the new firmware (188.8.131.52.00) can be downloaded by clicking here