If a nlwiki user donates from BE, their Thank You letter links to this page for cancellation instructions:
https://wikimediafoundation.org/wiki/Special:LandingCheck?landing_page=Cancel_or_change_recurring_payments&basic=true&language=nl-be
LandingCheck seems to fall back directly to English rather than looking for the page in nl, which does exist:
https://wikimediafoundation.org/wiki/Cancel_or_change_recurring_payments/nl