1. A machine implemented method comprising: identifying by a machine, within a document, a first language of a first portion of the document; identifying by the machine, within the document, a second language, distinct from the first language, of a second portion of the document; and performing a modifying function on at least one of the first and the second portions, wherein the modifying function is based at least in part on the identification of at least one of the first and second languages, and the modifying function checks a correctness of the identification of at least one of the first and second languages; wherein the correctness is determined by the modifying function based at least in part on errors detected when performing the modifying function; further comprising identifying by the machine, which of the first and the second portions is being operated on currently by a user and dynamically selecting modifying functions based on the portion being currently operated on; wherein the machine dynamically, as the user types in either of the first and the second portions, selects between a spell checker function for the first language in the first portion, and a spell checker function for the second language in the second portion.