Vim-accentuate is a project mainly written in Vim Script, it's free.
Vim plugin that transforms text with the Accentuate.us web service
accentuate.vim
Accentuate is a Vim plugin that uses the Accentuate.us web service to restore accents and special characters to text in over a hundred languages.
See doc/accentuate.txt for documentation and installation instructions.