“Frontier(s)” ends with a catfight. Under different circumstances, that might be winking fun. But in Xavier Gens’ flick it’s just the over-the-top end to a brutal, ridiculous ride. The French import, likened to “Saw” and “Hostel,” begins in the rioting streets of Paris. Promising. Yasmine, played by Karina Testa, above, and friends escape to the countryside only to land at an inn out of Eli Roth’s ouvre by way of “The Texas Chainsaw Massacre.” “Mais Oui!” Gens takes his initially smart riff on xenophobia and urban unrest toward the tiresomely familiar. “Frontier(s)” suggests sadism is the lingua franca of trendy horror. The unrated flick (with English subtitles) opens for a one-week run at the Harkins Northfield 18 before going to DVD (Tuesday, $19.98) where extreme-horror fans can love it in the privacy of their own dens of iniquity. Lisa Kennedy
