This might not be obvious at first sight, and I never had to do something like this, but it was a solution I've seen somewhere on the web and it's interesting in showing off how the TAL engine works:

<h2 tal:define="statusMessage python:request.get('statusMessage');
                   domain python:request.get('domain')"
       tal:attributes="i18n:domain domain;
                       i18n:translate string:">someText</h2>

(Taken from a weblog post)