"a wife is Lebanese" is somewhat not possible in Arabic. In such sentences of identification, usually the subject is definite in Arabic (i.e. with AL). While your subject here is indefinite. So, a translation of such sentence would probably depend on the context rather than being a direct one.
Anyway, the wife is Lebanese would be الزوجة لبنانية (with the predicative, or the word after "is" is typically indefinite in Arabic).