I know in the UK and many of it’s former colonies (exlcuding the US) lawyers as well as judges wear special robes in court. In UK and parts of Australia they still wear wigs. I saw the Reader the other day and was suprised that the lawyers were wearing black robes over their suits (which looked like morning dress). I though robes for counsel were just a British thing. Worldwide how common is it for lawyers to wear robes (or other special costume) while arguing in court? Is the US the exception in having lawyers wear ordinary suits? Are they countries were judges preside in business suits?
Don’t know about the rest of your question, but from what I’ve heard (about a year ago form my AP Government teacher FWIW, so it may not be correct) it’s becoming more common for judges to forgo the robe nowadays and just dress in a suit in the US. I’d say the robe is still more common and stereotypical, but we may see a switch eventually.
Even in England, home of antique lawyer outfits, many cases are heard with both the judge and the lawyers in suits, rather than gowns.
(Totally anecdotal experience: I spent a day watching cases in the High Court, where the ratio seemed to be about 25% robed/75% unrobed–if a judge was in robes that day, all cases before him were robed, and vice versa).
It depends on the court, and the type of hearing. As an example, the current court attire rules for barristers practising in the Supreme Court of NSW are available here: link (Click on the second dot point: Court attire policy)
I don’t know how often he wears it, but my father practices family law with the Ontario Bar, and when I was in his office the other day his court robe was hanging up, just back from the cleaners. So it is getting some use. I don’t believe he ever wears a wig though. I’ll ask him.
A (rather attractive) French lawyer wearing her robe. French prosecutor robe . President of a criminal court in full attire.
I don’t think wigs are worn anywhere in Canadian courts.
The usual rule for robes is that they are only required for the superior trial courts, the Courts of Appeal, and the Supreme Court of Canada. Even in these courts, robes are not worn by either the judge or counsel in chambers matters - only for the trial or appeal proper.
Counsel do not wear robes in the Provincial Courts (which have a variety of names across Canada), but the judge normally wears them.
If the judge is robed, then so too is the court clerk.
Note that our judges’ robes are more elaborate than are the American judges’ robes. There’s the long-sleeved waistcoat, the wing collared shirt, the tabs (what Rumpole calls the bands), and then the robe, which often has coloured facings.
And at the Supreme Court, there are the formal red robes, trimmed with white ermine, worn for the opening of Parliament, swearing in of judges, etc.
Northern Piper has it. I’m an Ontario lawyer, and I own (and on occasion, use) a set of robes. A wig would be awesome, but they are not used in Canada. 
In Spain they wear so-called “togas”. I am not quite sure but I believe the members of the court wear them with sleeves like this or this or seen from behind. I believe plain lawyers may not have the fancy lace on the sleeves. Or maybe it has nothing to do.
I ran a case once with some québécois lawyers, and they referred to their gowns (en français) as “toges”.
Here’s a picture from the website of the High Court of Australia, showing a plethora of barristers in their wigs and robes. The caption is:
As Cunctator says, it gets extremely fiddly. In UK and derivative jurisdictions where there is a distinction observed between barristers and solicitors, only barristers robe. The rules about the courts in which they robe are also fiddly. Sometimes (but generally not) they robe in the Magistrates Court. Barristers generally robe in the higher courts (District Court, County Court, Court of Appeal, High Court, etc) except for some types of appearances - usually the less formal applications, etc.
Assuming the circumstances call for robing, whether wigs are worn depends on the country (here in Australia, we generally wig…) the state (…but some states don’t) and the jurisdiction (some higher courts that robe do not wig). And some higher courts don’t wig themselves, but expect counsel to.
And then there is the question of which wig to wear…
It’s not really possible to understand the arcane rules about all of this unless you are in the trade and are a local to the jurisdiction about which the question is asked.
Judge in chambers a few weeks ago: “Why are you robed?”
Muffin: “Christmas office parties went to my waist.”