20. A system comprising: one or more computers and one or more storage devices storing instructions that when executed by the one or more computers cause the one or more computers to perform operations comprising: receiving data identifying source language text; receiving a translation for the source language text from a machine translation system, the translation including translated text corresponding to the source language text and segmentation data for the translated text, wherein the segmentation data includes a plurality of possible segmentations of the translated text, the plurality of possible segmentations dividing the translated text into a plurality of segments; receiving one or more alternative translations for each of the plurality of segments of the plurality of possible segmentations; and sending executable instructions that, when executed by a user device, cause the user device to perform operations comprising: displaying a user interface; presenting the source language text and the translated text in the user interface; presenting, in the user interface, a slider having a plurality of positions, each position of the plurality of positions corresponding to one of the plurality of possible segmentations; arranging the plurality of segmentations in an order from a smallest segmentation to a largest segmentation; and in response to a user input, presenting in the user interface each of the plurality of possible segmentations and the corresponding alternative translations for each of the plurality of possible segmentations, the user input providing for separately presenting each of the plurality of possible segmentations with their corresponding alternative translations, wherein moving the slider from a first toward a second opposed position of the plurality of positions displays the switching starting with the smallest segmentation and progressing toward the largest segmentation.
20. A system comprising: one or more computers and one or more storage devices storing instructions that when executed by the one or more computers cause the one or more computers to perform operations comprising: receiving data identifying source language text; receiving a translation for the source language text from a machine translation system, the translation including translated text corresponding to the source language text and segmentation data for the translated text, wherein the segmentation data includes a plurality of possible segmentations of the translated text, the plurality of possible segmentations dividing the translated text into a plurality of segments; receiving one or more alternative translations for each of the plurality of segments of the plurality of possible segmentations; and sending executable instructions that, when executed by a user device, cause the user device to perform operations comprising: displaying a user interface; presenting the source language text and the translated text in the user interface; presenting, in the user interface, a slider having a plurality of positions, each position of the plurality of positions corresponding to one of the plurality of possible segmentations; arranging the plurality of segmentations in an order from a smallest segmentation to a largest segmentation; and in response to a user input, presenting in the user interface each of the plurality of possible segmentations and the corresponding alternative translations for each of the plurality of possible segmentations, the user input providing for separately presenting each of the plurality of possible segmentations with their corresponding alternative translations, wherein moving the slider from a first toward a second opposed position of the plurality of positions displays the switching starting with the smallest segmentation and progressing toward the largest segmentation. 30. The system of claim 20 , the operations further comprising: receiving a user selection of a portion of the translated text; and receiving one or more alternative translations for the portion of the translated text from the machine translation system, wherein the executable instructions further cause the user device to present the one or more alternative translations for the portion of the translated text in the user interface.