The "Physician's Opinion / 医師が意見をかくところ" section of my Sickness and Injury Allowance application is written in a language other than Japanese. Is it necessary to attach a Japanese translation?

Yes, a Japanese translation is required.

The translation does not need to be an official, certified translation. However, someone other than yourself must create a separate document with the Japanese translation.

The translator should include the date of translation, their address, and their name (signature) in the margin or at the end of the document.