Force ASCII

[eluser]txomin[/eluser]
Not a CI question but please indulge me.

I'm developing a CI application for a Japanese school. They want everything in English and also want students to use "direct input", that is, ASCII. However, there is concern that some students might forget to do so and they want me to force them to do so via the code (as non-unicode desktop apps force ascii input on user). So, is it possible to create text fields, forms, etc that force ASCII input?

Thank you all in advance.