Can an Israeli Court dealing with Hague Convention proceedings authorize a voluntary return agreement that is not in Hebrew?

Yes! For example, in a Hague Convention case in which our legal practice represented the Mother (the Plaintiff) in 2014, the parents reached a negotiated settlement, in the form of a detailed written agreement, that was authorized, separately, in two languages and became incorporated into a Judgment, giving it full legal validity. The agreement was first authorised in Hebrew, at a hearing, in July 2014 and later the same month, in English, after the parties' counsel agreed on a parallel version/translation in English. (Krayot Family Court 40036-04-14).
Mediation & Agreement