In this paper, we propose a system for robust and flexible command interpretation on a mobile robot in domestic service robotics applications. Existing language processing for instructing a mobile robot often make use of a simple, restricted grammar where precisely pre-defined utterances are directly mapped to system calls. This does not take into account fallibility of human users and only allows for binary processing; either a command is part of the grammar and hence understood correctly, or it is not part of the grammar and gets rejected. We model the language processing as an interpretation process where the utterance needs to be mapped to a robot's capabilities. We do so by casting the processing as a (decision-theoretic) planning problem on interpretatory actions. This allows for a flexible system that can resolve ambiguities and which is also capable of initiating steps to achieve clarification.