The new provisions will enter into force on 1 January 2013, except the provisions concerning the loss of Belgian nationality, which come into force on 14 December 2012.
In short, as from 1 January 2013, foreigners who want to become Belgians must be in possession of an unlimited right to stay in Belgium, they must know a national language and be integrated. In addition to this: (1) it is no longer possible to become Belgian from abroad, (2) obtaining naturalization becomes more complicated and (3) maintaining citizenship is subject to more stringent criteria. The legislation also removes flexible provisions in relation to a fast track acquisition of Belgian nationality.
More information in the attached Belgian gazette (in French and Dutch only).