I hadn't counted on error messages with variable interpolations -- and I really should have thought about it. :( To properly internationalize this, we're going to need to do something like `_.template(gettext("Only {fileType} files can be uploaded. Please select a file ending in {fileTypeLower} to upload."), {fileType: this.attributes.fileType, fileTypeLower: this.attributes.fileType.toLowerCase()})`. Which is going to need restructuring the templates to expect internationalized strings, so it doesn't try to pass them through gettext twice. Ugh.

If you need to get this in quick, I'm fine with this approach for now, but the better way to do this would be to internationalize here. Sorry for my poor design decision when I made this.