If there is no language section for a school child that corresponds to the mother tongue or dominant language, the child is assigned to the "international section", which is officially called "Students without a language section". SWALS children are usually enrolled in one of the working language sections; their first foreign language is usually the language of that section. In order to promote the dominant language and their own culture, SWALS children receive additional tuition in their mother tongue and can receive learning support if necessary. This is only available for category I and II.
Further information on the language policy of the European Schools can be found here, on the subject of SWALS in particular Chapter 4 is of interest.