Software-language engineering is gaining momentum in research and practice, but it faces many challenges regarding language evolution, reuse, and variation. We propose language families, a feature-oriented approach to language engineering inspired by product lines and program families. The goal is to systematically manage the development and evolution of variants and versions of a software language in terms of the language features it provides. We offer a tool chain for the development and management of composable language features and language families. By means of a case study on the Web-programming language Mobl, we evaluate the practicality of our approach and discuss our experiences, open issues, and perspectives.