Hi Risto,
Thank you for your email and interest in supporting free knowledge. The Wikimedia Foundation, as a donor-driven organization, has a fiduciary duty to be responsible and prudent with its money. The Foundation does not currently accept Bitcoin or other currencies not backed by the full faith and credit of an issuing government. We do, however, strive to provide as many methods of donating as possible and continue to monitor Bitcoin with interest and may revisit this position should circumstances change.
Thank you again for your interest, and please feel free to contact us with any further questions.
Sincerely,
Joshua VanDavier
Donor Services Manager
Wikimedia Foundation, Inc.