Waited too longer to book tickets. English tours sold out for the period that we're in Budapest. Plenty of tours available in other languages. Has anyone taken the tour in a language they didn't understand just to see the interior of the building. How did that work out?
I took a tour in English. That said, if my only choice was another language, I'd do it. It is a pretty amazing place. Can you get a book or some type of resource to provide background and description of the rooms? I would try to familiarize myself with the building and go and prepare to be awestruck. I would also mention when you arrive that you couldn't get an English tour and maybe somehow they could accommodate you. I do recall that the person I purchased tickets from, on the date of the tour, spoke little English, but this was four years ago. The English tour was at 10am when I was there, if you are in the neighborhood, stop by before 10 perhaps?
I would just go over to the Parliament building, go to the underground ticket office and gift/coffee shop and see if they have any available tickets for the day you are there.
If not, just do the tour in another language, because speech about the place is not all that important, you can find out everything you really need by just reading websites. The big thing is being able to walk around and see the building on the inside.
PS. free WIFI down at the coffee shop.... and bathrooms if you enter from outside by the steps.