Try something like this:
$(function() {
$(".latin-only").keypress(function(event) {
if(!((event.which >= 65 && event.which <= 90) ||
(event.which >= 97 && event.which <= 122))) {
event.preventDefault();
}
});
});
If you want to allow spaces, add that to the statement above (|| event.which == 32). You will need extra logic somewhere (perhaps in a change event, or keyup) to remove illegal chars from the string when users paste a value into the input.
JSFiddle example.