Bala, as far as I know that feature is on the card but yet not publicly available.
Please explore these links:
This might also help out as well: Bringing the power of natural language to Tableau | Tableau Software
Essentially the GetData() call from the JS API can be use as an extensibility tool to connect Tableau with NLP tools already in the market. This is fairly broad topic with Tableau though, so you may need to do some research as to how you want to incorporate NLP into your analysis/deployment: this can range from sentiment analysis to natural language generation (machine generated commentary/annotation) and we would partner with different tools for each type of task.