"Ydw, dw i'n gallu seiclo."
Translation:Yes, I am able to cycle.
The word "bicycle" isn't here in the Welsh. The verb is "to cycle" cf MrGWall who is correct.
This sentence "Yes I am able to cycle" is standard English.
It is a different sentence from "I can ride a bike."
Checked with my tutor in Welsh at Cardiff uni who agrees with MrGWall.