How can I disallow non-English characters from being entered

Is there a way I can make it so my forms will not accept special characters not found in the English language? I basically only want to accept characters found on a traditional American keyboard. Is that possible?

I'm afraid that's not possible within JotForm. The only Validation you can achieve on a field level are the following:

Even if you select Alphabetic or AlphaNumeric as your Validation, users can still type in and enter non-English characters (e.g. Hebrew, Chinese, Japanese, etc) since all these languages are still considered Alphabetic.

It's worth mentioning that this can be done outside JotForm so if you have a developer, you can tell him about your requirement and have it added to your form's Full Source code.

Complete guide: How-to-get-the-Full-Source-Code-of-your-Form

Once he has the full source code, he just needs to programmatically prevent non-English characters from being entered using Javascript. To give him a head start, here's an example I found online while Googling around: http://jsfiddle.net/leniel/Fn9cy/7/