1) If you enter a wrong answer in the captcha question (sum), you will see a pop-up alert, writen in English : “The sum is incorrect”. This text is not adaptable using a translation plugin (CodeStyling Localization for instance). The text has to be edited in the source code of the theme.
2) When you enter a wrong answer in the captcha, all your data (name, e-mail and message) are deleted ! Not very userfriendly when you have written a long text, and you have to write again everything…