Skarpi,

There are many different versions of this song which is best know by its Gaelic title "Siúil a Rúin" which translates literally to English as "Walk my Secret" or more accurately as "Walk my Love". Some versions have the words "Siúil a Ghrá" in the chorus, which also means "Walk my Love". There have been many discussions here about the song under those titles.

There are a lot of versions of the song where people who didn't know gaelic just sang nonsense words instead of the gaelic, and the one you have given above is one of those.

I have no idea how this ever became known as the rainbow song, or Come the Rainbow, as none of the words have anything to do with that title.

The line which is sung in English as "Johnny has gone for a soldier" is "Go dté tú mo mhúirnín slán" which means "may you go safely my love".