KPMG informs us as follows:
During the summer holiday period, the Belgian VAT authorities usually grant an additional delay or grace-period for the filing of VAT returns. This means that VAT returns for the month of June and VAT returns for the second quarter may be filed by 10 August and VAT returns for the month of July can be filed by 10 September. However, no additional delay is granted for the payment of the balance of VAT due, its deadline remains the 20th of the following month, just as at other times of the year.
Similar rules exist in Denmark, Sweden and Spain.
(Hat-tip to Rob Hoeven)