What is the significance/theme of the repeated phrase Je ne parle pas francais in the story "Je Ne Parle Pas Francais" by Katherine Mansfield?

The title of Mansfield's story, Je ne parle pas français, is expressive of the lack of communication and social meaning in the main characters.

There is little, if anything, which reflects a culture more than a language. So, the "stale phrase" of Je ne parle pas français--I do not speak French--is thematic of Mansfield's stream-of-consciousness story narrated by the male prostitute, Raoul Duquette.  
This phrase, so commonly repeated by those who do not belong to the French culture, reflects the theme of sexual ambiguity--not belonging in a single sexual category-- since Raoul will go with men or women, as does Dick Harmon. Also, the woman called "Mouse" that Dick brings to Paris has some manly traits, such as her "boyish" hands. Her act of holding out her hand "in that strange boyish way Englishwomen do" also conveys a certain sexual ambiguity. 

A story set in post World War I, a time in which France lost its moral center just as did other countries, "Je ne parle pas français" has a narrator and main character, Raoul Duquette, who hedonistically focuses solely upon the satisfaction of his own desires. He presents himself as a writer, but in reality he merely uses this pretense to frequent a cafe where he can prostitute himself to women or men, although he never propositions them. The title phrase, Je ne parle pas français, then, is also expressive of Duquette's amorality and nihilism, the belief that life is without real meaning, purpose, or intrinsic value. He simply enjoys what pleasures he can while acting under the pretense of having a literary profession. In essence, then, he does not really speak French, a historically precise language of philosophy, love, human truths, and war. 

Another theme of Mansfield's story is that of the masque. Certainly, Duquette wears a social mask as he is not truly a writer, as he pretends. As an example of his pretense and self-deceit, at one point in the story, he narrates that he stands before his mirror, practicing his pose as a "man of letters." After all, he decides, if a person looks the part, he must be that part. Clearly, then, Raoul does not speak the language of reality; he merely pretends to do so.
Dick Harmon, also, pretends to be other than what he is. He masques as a heterosexual man, but has relations with Raoul, and is involved in some sort of odd relationship with his mother. For, he abandons the woman who believes he will marry her, writing her a letter that explains that he is controlled by his mother, whom he writes to Mouse as "dragging me back to her--calling."