Is it permissible to learn Hebrew to enable one to debate with the Yahood and to prove them wrong from their own scripture?

Answer

It is a Shaitaani ploy to study Hebrew. The desire to want to debate with the kuffaar is also a snare of Iblees. One should not have such desires which detract from the Aakhirat. Shaitaan approaches people via 'deeni' channels to derail them from Siraatul Mustaqeem.

Rasulullah (Sallallahu alayhi wasallam) expressed considerable anger when he saw Hadhrat Umar (Radhiyallahu anhu) reading even the Tauraah which at that time contained a great deal of Ilm-e-Wahi.

The indulgence in dubious 'da'wah' activities is most certainly a gross waste of time and brains, and this is a grievous sin. Indulgence in futility is not permissible.