From what I recall of the scholarly version of this story, in particular the history of the name, the Sanskrit "Bodhisattva" was interpreted in a Manichean version of the story, written in I think Pahlavi (an Iranian language close to Persian), as "Bodisav". From the Pahlavi it received a Muslim Arabic version originally as "Budhasaf", but a typographical error resulted in "Yudhasaf" in later versions, since the Arabic letter for "b" is very similar to "y" (the difference being in whether or not two dots are written above the character). The first Christian version was the Georgian "Iodasaph" in the 10th century, later rendered in Greek in the 11th century as "Ioasaph", and finally when it got its Latin version the name was changed to the similar-sounding, originally Hebrew "Iosaphat". I'm not sure if Ioasaph is originally Hebrew, or if it were chosen just because it sounded like "Iodasaph". If the latter, I don't understand what happened to the Georgian "d", since Greek has a sound similar to "d". Why delete that sound? Perhaps someone with the time to read the original scholarly literature can tell me.
I have to say overall the scholarly story sounds pretty plausible, when the dates of the various versions are lined up after one another and you can trace the slight developments in the name and the story elements over time. I still would not feel too comfortable just accepting the account without any personal expertise in the matter, since I know how easy it can be to manipulate this kind of historical evidence to make a plausible and coherent story, when in fact the original raw evidence may be less compelling. Plus there's the awkward fact that the veneration of SS Barlaam and Ioasaph is now pretty well established in the Church, and story as we have it is rather different from the original story about Buddha. I guess it's kind of like creation and evolution and other cases where Tradition just doesn't fit with modern scientific or historical scholarship. I don't think there's much to do but try to give the Church the benefit of the doubt, while acknowledging that there are difficulties in reconciling the Tradition with our attempts at reasoning.