CAPTCHA Manual Translation for multi-language site

Hi all,

I am working on a multi-language site, and I’d like to have different languages set for the Contact Forms in different parts of the site.

I created a new plugin using this code to change all form CAPCHAs to Croatian language:

add_filter('avia_contact_form_elements', 'avia_change_caption_captcha', 10, 1);
function avia_change_caption_captcha($form_fields)
{
        if(!empty($form_fields['avia_age']['label'])) $form_fields['avia_age']['label'] = "Potvrdite da niste robot unošenjem točnog iznosa.";
    return $form_fields;
}

But I need them in Croatian in some parts of the site, and English in the others. I’d also like to expand to other languages later on. For example:
http://mysite.com/en/
http://mysite.com/hr/

Thanks in advance.