It could be done with fields, but I would not say there is less maintenance with that. Just no userforms or macros required.

My suggestion would be to have the optional language in AutoText entries and use IF fields and AutoText fields to pull in the optional text. That way you can standardize language and to modify it you update the AutoText entries rather than the fields. It is still going to be a maintenance headache. Also, the IF fields would need to be updated. (And I would likely recommend a macro to do that.)

A key question is whether everyone using it is using Word 2007 or later.