Since OS X Mountain Lion, Dictation has enabled the use of voice as an alternative to typing text. Dictation’s voice recognition process is similar to Siri’s and hence continues to require an active internet connection to function as Siri does in iOS.
Today OS X Mavericks quietly introduced an extension to Dictation called Enhanced Dictation. With Enhanced Dictation enabled, voice recognition will be available offline including synchronised textual display known as Live Feedback. Approximately 800MB will be downloaded when the extension is enabled. Dictation, including Enhanced Dictation, is available in 8 languages (Chinese, English, French, German, Italian, Japanese and Spanish) along with the various dialects.
Siri in iOS could be next.