In case you will use the Belgium system to build up a pension, be aware that Belgian pensions are financed by three pillars. Make sure to examine the possibility of the second and third pillar, that are not mandatory, if you would like to receive a higher pension.
Also bear in mind that the pension age, conditions and amounts will vary depending on whether you are employee, an independent worker or a civil servant.
Contact the Federal Pension Service if you have any more questions on this matter.