1. A computer-implemented method, comprising: receiving, at a viewing application executing in a foreground at a computing device, a touch input from a user, the touch input comprising: (i) a first portion indicating a selection of a single selected word in a document in a source language, the document being displayed in the viewing application, wherein the viewing application is not configured to perform language translation; and (ii) a second portion following the first portion and indicating a trigger command for obtaining a translation of the selected word from the source language to the target language; and in response to receiving the touch input: obtaining, by an operating system executing at the computing device, contextual information from at least a portion of a full screen capture of the document, wherein the full screen capture includes an entire viewable area of the computing device, wherein the portion of the full screen capture is associated with the selected word, and wherein the contextual information is indicative of a context of the selected word as it is used in the document; extracting, by the computing device, contextual features of the selected word using the contextual information, each contextual feature being a machine-learned feature indicative of a use of the selected word, wherein the contextual features include both (i) one or more first words from at least the portion of the full screen capture and (ii) an image from at least the portion of the full screen capture, wherein the image does not include the one or more first words and the selected word; providing, from the operating system and to a different translation application, the selected word and its contextual information, wherein receipt of the selected word and its contextual information causes the translation application to obtain and output potential translated words to the operating system, wherein the translation application (i) is distinct from the viewing application, (ii) is launched by the operating system in a background at the computing device or is already executing in the background at the computing device, and (iii) is configured to obtain the potential translated words using the selected word and its extracted contextual features; providing, from the operating system to the viewing application, the potential translated words, each potential translated word being a potential translation of the selected word to a different target language that is preferred by the user; and displaying, by the viewing application, the potential translated words.
9. The computer-implemented method of claim 1 , further comprising: transmitting, from the computing device and to a remote server, the selected word and its extracted contextual features; and receiving, by the computing device and from the remote server via the network, the potential translated words.