I think your project would be much easier to do in Publisher.
You can set up two different text boxes (one on the top half of each page for the text in the one language, and a second on the bottom half of each page for the corresponding translation) which will continuously run from page to page. When you add, delete, move or modify, the text automatically moves about through the pages. Also, let us say you wanted to change the font size for the entire text box, you go into that one text box (any page), hit Ctrl-A to select, and it selects all of the text in that box on ALL of the pages.
The simple trick is doing a little bit of planning and then initially setting up the two text boxes properly; Publisher will automatically link them for you. If you can comprehend the concept behind how Publisher thinks, it will be easier to understand why it does what it does and puts things where it puts things.
However, before I go into the details, I have a few questions. Any of these answers/settings can be changed at any time but your responses will be helpful to me to get an idea of what you want for an end result.
What are your page margins?
Are you going to want headers, footers and/or page numbering?
Approximately how many half pages do you think your information will span?
About how many pages do you think you have already to insert into the text boxes (they can still be edited)?
Do you have any experience at all with any version of Publisher?
What is your time frame for getting this set up accomplished?
Additionally, regarding the info you want on the top half of each page, it that in its complete or near complete stage in Word already?
Based on your answers, I will first quickly set it Publisher 2003 (because I am extremely familiar with that version), then go over to my husband's computer which has Publisher 2007, and figure out how to produce the same results. Then I will be able to provide you with some not-too-complicated instructions for your set up. [Or if it is easier, I can provide blank layout pages and all you will have to do is cut and paste your info into each of the two text boxes.
Another advantage to using Publisher is that you can insert other pages that can have their own unique text boxes for things like a title page, introduction, etc.
However, PLEASE let me know if I am on the right track. Is what I have said above what you want to accomplish? If not, I would appreciate it if you could please provide me with more details in order to save us both time.