Migrating programs between language versions is a daunting task. A developer writes a program in a particular version of a language and cannot foresee future language changes. In this article, we explore a solution to gradual program migration based on virtualization at the programming language level. Our language virtualization approach adds a backwards-compatibility layer on top of a recent language version, allowing developers to load and run old programs on the more recent infrastructure. Developers are then able to migrate the program to the new language version or are able to run it as it is. Our virtualization technique is based on a dynamic module implementation and code intercession techniques. Migrated and non-migrated parts co-exist in the meantime allowing an incremental migration procedure. We validate it by migrating legacy Pharo programs, MuTalk and Fuel.