Here is a post from Stephan Huller explaining where the Talmund gets the odd name Jesu or “Yeshu” from:
The rabbis came into contact with ‘Yeshu’ in the Semitic Christian cultures of the East. Because Syriac does not use the ‘furtive’ pathach (see link below) Yeshua the shortened form of the name Yehoshua would be naturally rendered Yeshu (i.e. so the ‘a’ vowel is not used). This follows a pattern noticed with respect to other Hebrew words rendered in Syriac. The third and fourth century rabbis must have come across the name Yeshu and found it puzzling or decided to preserve the unusual form in their Aramaic reports about their Christian neighbors. It does not provide any window into the original name of Jesus as it represents only a transformation of the short form of ‘Joshua’ into Syriac.
Why is this particularly significant? Because this possibly gives us a terminus post quem for when non Greek/Latin speaking Christians started interacting with or trying to convert Jews. But the knowledge of this odd spelling seems to go back further than the 3rd century. This is Irenaeus writing in the late 2nd:
Moreover, Jesus, which is a word belonging to the proper tongue of the Hebrews, contains, as the learned among them declare, two letters and a half, (ישו:: Y-SH-W)
I’m thinking that this gives weight to the idea that Jesus actually wasn’t that well known among the Pharisees who supposedly had him crucified. The traditions of the Pharisees are where the traditions in the Talmud come from. We already have evidence of this from the possibility that Pharisees historically had very little to no presence in Galilee. So the popular gospel image of Pharisees stalking Jesus there would necessarily be an invention.
So if Pharisees had actual eyewitness experiences with Jesus, or traditions that actually went back to Jesus, then they would have retained his actual Aramaic name Joshua and not used the derived Syriac name Yeshu. This also seems to corroborate the idea that Jews did not know about Jesus until Christians started preaching about him.
Finally, the Islamic name for Jesus, Isa (or Yasu), seems to be derived from the Syriac, as Syriac Marcionites called Jesus Isu.