So the fluff is fairly clear regarding how Imperial nobles are generally treated within the Empire. They're somewhat above the law (unless messing with their peers), commoners generally go out of their way to appease them, and so on.

But what about foreign nobles? Are they afforded the same leeway or are they treated like any other foreigner?

I ask because I'm planning a story arc which will at one point involve an obnoxious Bretonnian Knight Errant 'questing' through the wilds of the Empire, and I'm not sure as to how the locals should be expected to react to him.

Any insights would be greatly appreciated; my thanks in advance.

Hm, it can go either way. The thing is a common person in the empire would have two ingrained behaviours working in opposition. On the one hand; you allways respect your betters, if you know what's good for you. On the other hand; you hate foreigners. So the question is, is he your better?

A foreign noble will probably often be in the Empire to meet emperial nobles. Then the point becomes mostly moot. He is an Empire noble by affiliation. Maybe Sir Frogeater of Bretonnia doesn't have the social clout to demand your respect, but his friend Baron I-tax-you-however-much-I-please might hear of you disrespecting his guest. So it's best to just treat him like an empire noble. And you don't allways know if this is the case or not, so it's best to not antagonize nobles either way.

In addition, a noble person is also usually a person of means. So you might dial back on the xenophobia in order to fill your pockets. But you might try just a bit harder to trick some extra money out of him. Him being a dirty foreigner and all.

On the other hand, as a foreign noble you have a lot less leevay when it comes to being accused of crimes. If you do not have any obvious connections to imperial nobility you are a lot more likely to become the target of angry mobs, since you have noone to speak in your favour.

Ralzar made some great points.

I would just like to add that in some instances the commoners of the empire might not even recognize the knight as a foreigner, at least not at first sight. If he knows riekspiel well enough (or just doesn't talk to pesants) they might only see fancy clothes, a warhorse and expensive armour and conclude that he's a noble knight and treat him with respect/awe, especially if it's far from the border to Betonnia.

But then again he might be recognized as a foreign knight on sight, especially in larger town or cities. It could be vary a lot from place to place.