1. A computer-implemented method, comprising: receiving, at a computing system, audio data that indicates a first voice input that was provided to a computing device; determining that the first voice input is part of a voice dialog that includes a plurality of pre-defined dialog states arranged to receive a series of voice inputs related to a particular task, wherein each dialog state is mapped to: (i) a set of display data characterizing content that is designated for display when voice inputs for the dialog state are received, and (ii) a set of n-grams; receiving, at the computing system, first display data that characterizes content that was displayed on a screen of the computing device when the first voice input was provided to the computing device; selecting, by the computing system, a particular dialog state of the plurality of pre-defined dialog states that corresponds to the first voice input, including determining a match between the first display data and the corresponding set of display data that is mapped to the particular dialog state; biasing a language model by adjusting probability scores that the language model indicates for n-grams in the corresponding set of n-grams that are mapped to the particular dialog state; and transcribing the voice input using the biased language model.
7. The computer-implemented method of claim 1 , further comprising receiving, at the computing system, an application identifier that indicates an application to which the first voice input was directed at the computing device, wherein the plurality of dialog states pertain to an application-specific task for the application to which the first voice input was directed.