The dialogue of J.M. Synge's The Playboy of the Western World is important to the play because of its root in realism. Realist writers wished to show the world as it really was. They tended to act as observers who recorded what they saw around them without interpretation or intervention. Their works were illustrations of how life was.
The dialogue of the play illustrates this idea. Synge included the slang and language of the people he was describing. The language is distinctly Irish, like the author and playwright. Study in Irish language shows the reality of the play's dialogue and characters. For example, when Christy speaks of the "divil," one can hear the nuances of the language.
An extended look at the dialogue of the play would include textual examples of Synge's native language, meanings, and importance of their use in order to ground the play in reality.