From a global and historical perspective, multilingualism or at least multilectalism is the rule rather than the exception. However, linguistic theory continues to focus on the idea of a prototypically coherent, static, and monolingual language system. A more realistic approach can set out from the notion of ‘diasystems’, i.e. linguistic systems including more than one variety. Apart from being theoretical constructs, diasystems are also an important component of multilectal speakers’ linguistic knowledge. Within a usage-based construction grammar approach, this paper argues that multilectal speakers (re-)organise their grammars by generalisation over individual constructions and across language boundaries. Therefore, the multilectal system can be modelled as an inventory of constructions that are partly language-specific and partly unspecified for language.