Making use of Tornado's locale functionality in WTForms. By Ben Darnell.

forms.py

import tornado.locale
from wtforms import Form, TextField, PasswordField, SubmitField, validators


# Later use e.g. FORMS['es'].LoginForm
FORMS = {}


error_msgs = (
    'You must enter a username.',
    'The username must atleast be one character long and can\'t be longer '
        'than 25 characters.',
    'You must enter a password.',
    'The password can not be longer than 255 characters.',
)


# Call this after tornado.locale.load_translations
def create_forms():
    for code in tornado.locale.get_supported_locales(None):
        _ = tornado.locale.get(code).translate
        class FormNamespace(object):

            class LoginForm(Form):
                username = TextField(_('Username'), [
                    validators.Required(_(error_msgs[0])),
                    validators.Length(min=1, max=25, message=_(error_msgs[1]))
                ])
                password = PasswordField(_('Password'), [
                    validators.Required(_(error_msgs[2])),
                    validators.Length(max=255, message=_(error_msgs[3]))
                ])
                submit = SubmitField(_('Log in'))

        FORMS[code] = FormNamespace