Of course, The Search for Spock is a spoiler, but it's clearly intentionnal. I rembember when I was a kid in the late nineties. Some Quebec's trekkies had been invited at a TV show and the hostess asked if Spock would be in the incoming movie (Insurrection). When my parents rented First Contact, my mother asked if the Vulcan at the end was "captain Spock". For the general public, Star Trek = Spock, so, for the producers, Spock = $pock.
French translation of titles are generally good for Star Trek movies, except the fourth were they missed the thing. Retour sur Terre, it's litterally Return on Earth and we finally discover that the home was an Enterprise commanded by Kirk.
Final Frontier is not an innapropriate name, but it could have been the title of the sixth. What's the biggest deal, the most extreme thing that Kirk could have done? Finding God or making peace with Klingons?

I suggest "Star Trek V: The Secret Half-Bro Who Turned Charismatic" or "Camping, Horse Riding and Stripping".
Oh, and for Nemesis, I would have chosen something more linked to Romulus and Remus as mythological figures or about the rage of a bald cybergoth dragqueen who becames the dictator of the people he hates so much.