The new option to translate a document becomes available after clicking on Tools > Translate Document in the header menu while viewing a single document in Google Docs.

Available is the usual assortment of languages that is offered by the Google Translate service. Selecting one of the languages in the menu will open a new window that displays the translated text after a short time. It is then possible to create a new document based on the translated document or replace the existing document with the translation.

The document cannot be edited in this window though. This option becomes available after selecting one of the two options described above. It would have been nice if Google Docs offered at least some form of export and editing capabilities right away so that users who want a quick translation of a document can process it further without having to save it first before they can do so.

Another option that is currently missing are partial translations of documents. It’s currently either all or nothing.

source official Google Docs Blog