I am trying to make a dual-language ebook. I'd like it to be typeset in two columns with one language on the left and the other on the right.

Is this possible with the epub specs?

• epub

It is quite possible, with two different ways:

1. Columns (used by wikisource epub export):
   • You can try with the printable version of this page (choose epub of course) : http://fr.wikisource.org/wiki/Trait%C3%A9_de_la_r%C3%A9forme_de_l%E2%80%99entendement_%28bilingue%29
   • On my Kobo, the regular epub engine screws the cells (the end of cells, if out of the display, is just ignored...) so you need to rename your epub file into .kepub.epub for the adobe engine (I guess) to be used and a correct display to be used.
2. Interlinear:
   • Using a simple css trick (display:inline-table) you can have different lines / words one under the other.
   • I have made a chinese version with chinese, pinyin and translation quite easily.

Hope this helps.

I'd use a simple table.

If you were thinking about CSS columns property : it is unreliable on iBooks and not even implemented on ADE based devices.