What you are doing sounds about right.

I would have each used paragraph style in pairs where there is an english and spanish variant. For instance 'Heading 1' and 'ES Heading 1'. If you prefix the spanish styles they will all sit together in the style list to make things easier. Put everything into a 2 column table and keep a language on each side. If your pictures are not language-specific, you could place them in a row and merge the cells so you get full width graphics.

You will be able to build separate English and Spanish Tables of Contents because of the styles and spell check each paragraph in its own language.

As long as you are consistent, you will be able to copy a column and paste to another document to get a single language version. The merged rows will allow those rows to be in both column selection variants.

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Andrew Lockton
Chrysalis Design, Melbourne Australia