With the growing use of domain-specific languages (DSL) in industry, DSL design and implementation goes far beyond an activity for a few experts only and becomes a challenging task for thousands of software engineers. DSL implementation indeed requires engineers to care for various concerns, from abstract syntax, static semantics, behavioral semantics, to extra-functional issues such as run-time performance. This paper presents an approach that uses one meta-language per language implementation concern. We show that the usage and combination of those meta-languages is simple and intuitive enough to deserve the term "mashup". We evaluate the approach by completely implementing the non trivial fUML modeling language, a semantically sound and executable subset of the Unified Modeling Language (UML).