Oh my, those logos are absolutely atrocious! Never mind the translation: the text is clipped to incomprehensibility anyway (at least when displayed in firefox) -- and that includes the english language one. On the plus side, these logos are so obviously bad that I don't think anybody reasonable will consider using them.
Concerning the dutch translation: Especially for professional/business terminology, the Netherlands have a strong preference for just borrowing the english term (this may be a bit different in Flemish-Belgium), so "open source mathematics" or "open source wiskunde" sounds completely acceptable to me. The most direct translation "vrije broncode wiskunde" sounds a little strange. It would need to be "wiskundige software met open broncode" which doesn't really have a punch. Using "bronnen" (sources) has no software association in dutch at all, so it would seem that it's about mathematics that uses available (historical?) sources rather than secret ones.
As anecdotal evidence of use of english terms in official dutch communication meant for a dutch audience:
(note uses of "open source", "ICT" (meant as an english acronym, although a translation would have the same letters). Indeed, a good effort in using the word "broncode" in various places.