Mac OS X Mavericks Offline Speech to Text Dictation Feature
Apple introduced Siri for iOS and Text dictations in iOS 6. This dictation feature was introduced in OSX Mountain Lion in year 2012 but the problem was you constantly needed internet connection to use it and was quite buggy. And the data was sent to-and-fro to the servers to get the results, and could hardly convert speech-to-text for only few words at a time.
Now for Mac OSX Mavericks Apple has introduced a option in "Dictation & Speech" that lets you dictate offline. It is called as "Enhanced Dictation"
Steps to configure offline Dictation in Mac OS X.
-
1. Go to Spotlight Search and type and open "Dictation & Speech".

3. Now you need to download offline package for dictionary, Select the Language that you want speak it.
Office package size depending upon what language you choose, You can even see that there are different accents/dialects available for languages like English, French, Chinese , German , e.t.c.
-
Language Options Available :
1. English (United States) : Download size : 785 Mb
2. English (UK) : 491 Mb
3. English (Australia)
4. English (Canada)
5. Japanese (Japan)
6. Chinese (China) : 321 Mb
7. Chinese (HongKong and SAR China) : 413 Mb
8. Chinese (Taiwan) : 321 Mb
8. Spanish (United States) : 547 Mb
9. Spanish (Spain)
10. Spanish (Mexico)
11. Korean (South Korea)
12. French (Canada)
13. French (Switzerland)
14. French (France)
15. German (Germany)
16. German (Switzerland)
17. Italian (Italy)
18. Italian (Switzerland)
4. Once downloading is done ,you can try doing a dictation by using the Dictation & Speech shortcut (by default it is invoked by Fn key Pressed Twice, if not sure you can check it in Dictation & Speech next to Shortcut).