The point Chesterton was making was that we shouldn't feel that just because something is foriegn we ought to be ashamed to admit that we find it funny. Not quite the same as finding siomething funny just because it is foreign.

If, for example, a French vistor finds Morris dancing funny, is that more shameful than if an English native thinks it funny? Or if a Morris dancer actually glories in its being funny?

Most people are funny much of the time, and the things they do are funny much of the time. Sometimes familiarity takes off the edge, so we don't recognise how funny they are. The effect is that it can be easier to recognise the absurdity of life when it is mediated through things that are unfamiliar, for example, foreign.

The crucial thing is that just because we find something funny, that is not a reason for thinking it wrong or despising it.