User blog comment:Oppaichan/Bilingual or Booblingual?/@comment-16281343-20150711130916

As I've got the time to investigate this one, here's my finding.

The correct one should be パイリンガル (ppai-lingual).

Ishibumi's hasn't entered the word on his twitter nor his blog, so we don't have any official proof BUT the whole Japanese community calls it パイリンガル (ppai-lingual) ; never バイリンガル (bilingual).

To give some perspective on how this somebody make a mistake on reading the name, here's the technique's name on the v19 raw (granted that the quality may change with the book.)