Solved.
The problem is the jQuery plugin Swiper – it blocks the form fields.
Answer: declare the parameter “releaseFormElements: true” on Swiper initialization.
I use this code in my template:
<?php echo do_shortcode( (qtrans_getLanguage()=="en") ? '[form en]' : '[form pt]' );
There’s a little problem: when I use the english form, after submit return to english form. When I use the portuguese form, after submit return to english form. And I don’t know why.