tl;dr
As long as the pendulum can oscillate reliably, the Foucault Pendulum rotation is independent of the strength of gravity.
If your question is about a normal pendulum and you didn't actually mean to talk about the Foucault Pendulum phenomenon, then a normal pendulum will still work even in very weak gravity in a reasonable way, as long as the length of the pendulum is significantly shorter than the diameter of the body and the body is at least roughly spherical and you're at the surface.
Backgound
Based on comments under @Uwe's answer such as
I'm not asking "how must it be build to work on x planet" but whether it can actually oscillate on extremely-slowly-rotating planets like Venus.
and
Mercury or the Moon don't have significant atmospheres, therefore there's no friction. Isn't the duration of oscillations also dependent on how strong the gravity is?
I'll elaborate.
The period of one swing of a pendulum is
$$T = 2 \pi \sqrt{\frac{L}{g}}$$
where $L$ is the length of a pendulum and $g$ is the gravitational acceleration. Flip it around and get
$$L = \frac{g T^2}{4 \pi^2}$$
If $T$ is 10 seconds then $L$ is about 25 meters on Earth and somewhat shorter on bodies with smaller surface gravity.
This is almost completely unrelated to the rotation rate of any reasonable body.
The Foucault Pendulum phenomenon is related to the rate at which it very slowly precesses or the plane that the pendulum oscillates seems to slowly rotate relative to the ground.
Imagine you are at the South pole and you set up a really well protected, lossless pendulum. The plane of its oscillations will appear to rotate once a day. It's an apparent rotation, not an "oscillation".
It's not real though, if you viewed from space you'd realized it's really the Earth rotating underneath the pendulum, and the pendulum's plane isn't rotating at all.
If you move to a lower latitude, now the plane will start to rotate a bit even seen from space. If you are on the equator the plane rotates once a day (assuming it's North-South) but from the planet it won't be seen to rotate at all.
Answer
The rate of rotation of a Foucault Pendulum as seen on a planet is always some fraction between 0 and 1 times the planet's rotation, and has nothing to do with the strength of the gravity.
As long as the pendulum can oscillate reliably, the rotation is independent of gravity.