where to access the text on ProSites "subscription plan 1-3-12- monthts buttons" for loaca

Hello all, can´t find the corrensponding file in order to change the text for the 1-3-12 month subscription payments plan buttons shown on page "http://.../pro-site/?bid=1"
Need to change this text into German - didn´t find it in the *.po file - had a quick look at the code with firebug and the impression the text is input via php, just ran out of ideas where to look for... thanks!