This essay for the inaugural issue of Technology and Language shows that the mastery of multiple languages is the enabler for good engineering design. Engineers express ideas and for that they need expressive design languages. If a language is a structured system of symbols serving communication, the languages of engineering include German, English, and Russian, mathematical and programming languages, technical drawing and formal modelling, with abstract design elements constituting a further, engineering-specific language. The semantics and thus the basic elements of these languages constitute the design space, whereas the syntax constrains the expressivity of the language and structures the design space.