Dermot Mulroney -- Wife Ditches Maiden Name ... But Still Not Taking His

Dermot Mulroney's wife desperately wants to go French -- even though her husband is Irish-American -- and she's filing legal papers to do it.

The "My Best Friend's Wedding" star has been married to Tharita Cutulle since 2008, but she's never changed her name. According to docs, she's finally ready to drop her unique name and switch -- not to Mulroney ... but to Prima Apollinaare.

As for why she's going from sounding like the scientific name for a fish ... to a fancy pasta? Maybe she's a theater buff. Guillaume Apollinaire was a famous French poet and playwright in the early 1900s.

Or maybe she digs Apollonia from "Purple Rain." 'Memba her?