Ah, law levels. Where should I even begin. The basic concept is the same as with the other characteristics of a mainworld. Roll 2d6-7, this time adding the government value to the roll. I think the concept is as old as Traveller, and nobody ever bothered to revisit it – which is just as well, because I again think that this is too varied a topic to just solve with one roll.
For example: The law level table has six categories, but a society doesn’t necessarily restrict different types of item to the same degree. For instance, Germany does restrict weapons (law 8) but has a free press and really no restrictions on software (Information law level 0-3 depending on your view).
Finally, I think that directly basing it off the government value is… problematic. While the government table is ordered roughly in such a way that more “liberal” societies are associated with lower government characteristic numbers, and more repressive ones with higher numbers, I don’t think this necessarily means that they oppress everything in massive ways. And there are strange exceptions; for example a “captive government” is code 6 and those tend to be fairly restrictive.
A better way is perhaps to assign each government type a specific DM, and then roll for each column separately. Then use the highest value in the UWP. Of course this results in a lot of extra data and that will dilute the simplicity of the universal world profile.
What I Will Do
I will roll for law levels normally, but I will not take the value as a rule. Instead, it will be a guideline, indicating whether a planet is more liberal or more restrictive than the norm. Then, once I have worked out the general law level of the interstellar polity each world belongs to, I will rework the values to make sense.