1. A computer-implemented information retrieval system comprising: a query component configured to receive and process a query to retrieve a document having different language styles as data streams, the data streams including at least a first stream for a first portion of the document and a second stream for a second portion of the document, wherein the second stream is different from the first stream and the second portion is different from the first portion; a model component configured to create multiple language models for the data streams of the document, the multiple language models characterizing the data streams for document ranking, the multiple language models comprising at least a first language model for the first portion of the document and a second language model for the second portion of the document, wherein the second language model is different from the first language model; an estimation component configured to estimate mixture weights for the multiple language models; a smoothing component configured to apply smoothing to the multiple language models to generate similar cardinality among the multiple language models for linearly combining scores output by the multiple language models; and a processor configured to execute the query component, the model component, the estimation component, and the smoothing component.