Yeah, the english dubbings in most exploitation films is indeed silly for the most part (you DON'T want to watch a Max Pécas movie in english. I know the man had a wacky sense of humour, but in french it really doesn't sound ridiculous!)
But, as for Franco, most of the productions were dubbed anyway - for example, in "Nightmares come out at night" I own the spanish DVD and the audio that makes more sense is the french, not the spanish. I guess that, according to the scenes, different actors spoke different languages - and then it was all dubbed. So, I guess that for most Eurocine productions the way to go is in french and for the Erwin C. Dietrich ones (Jack, the Ripper) in german (if it comes with subs - great that the UK DVD has them, shame that the VIP releases don't, as they're all uncut).
I remember having seen "Love Letters of a Portuguese Nun" in the cinema in 1986 (or around that) and though I can't remember it quite well, I'm pretty sure it was in german. It was unforgettable, because some of the cast are very known actors in these parts (one of them - the prince - is a major comedian and star on portuguese TV, and so was Ana Zanatti - the mother superior - in the 80's) and it was funny that they were dubbed. Even funnier is that all of them dismiss into oblivion their participation in the movie :)
Well... They're wrong! It was the first Franco movie I saw and it got me hooked.