In a document that is predominantly in one language, you might define one language for proofing the document as a whole, then use a character Style set for proofing in the other language and apply that to any text in the other language. In a document that mixes two or more languages with none being truly dominant, you might define separate paragraph Styles for each language as well.

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Cheers,
Paul Edstein
[Fmr MS MVP - Word]

Thanks. Mine is actually worse that that! It's more or less like a Spanish-English dictionary. Although English words dominate, there are just too many Spanish words scattered around. I can't highlight each Spanish word on each page and apply a separate style to them. Well, I can, but it would take too long.

I thought about cramming a small Spanish dictionary into the custom dictionary. But that would only contain words in their dictionary forms (e.g., palabra would be included but not palabras).