Is dressing oneself in formal attire on Sundays (Sunday hat and dress) solely an American Christian custom? Before I start, I realize that this question is related to another question. However, this question is more concerned about the custom of wearing one's "Sunday best", which usually means a nicely brimmed Sunday hat and modest-looking dress. This has been portrayed in literature and in movies. Example: Chicken Sunday, written by Patricia Polacco, and Bridge to Terabithia (2007 movie). Is this solely an American Christian custom? Are there examples in other Christian cultures? How did this custom come about, and how did it evolve over time?
I am unsure as to most other Christians. Among those that I have studied with and continue to study with they have always dressed formally. 

I believe that Christians of any denomination dress nicely when going to worship god. It's part of giving god your best. Here in an article that may explain a bit better and I think it is relevant not only to witness', but all Christendom. Why dress up for meetings

This doesn't mean your clothes had to be expensive. As long as you are clean and presentable then that is acceptable.

It seems as far as history goes Christians not only wore, but where encouraged to wear simple clothing so as to not distract from the meaning of the occasion. This is especially true in the 18 and 19th centuries. Worshipers usually dressed plainly with no ornate jewelry and such. This is not only for the reason stated above, but that your everyday person didn't have the means to come by these things.

Origins /3rd Century changes / Why dress nice? 

Based on a little more research it seems dressing up was a social status thing and then later became a part of representing and honoring god.