The pattern language concept, adapted from building architecture and detailed software design, has recently been applied to HCI by a number of researchers. We argue that the "language" aspect of pattern languages is critical and outline thirteen research efforts in HCI patterns. Many pattern collections have broad scopes, and we argue that this results in patterns which are not as interdependent as a narrow scope would allow. The argument is illustrated with our Planet pattern language, which helps developers reuse knowledge for internationalised software. The narrow scope, namely a focus on the needs of internationalised users, allows us to produce interdependent patterns which range in abstraction level, from organisational process to high-level specification to detailed software design. Thus, the language supports a generative, interdisciplinary, approach to reusing knowledge in HCI.