When we want to say "in the style of" in Italian, why do we use the feminine form? I mean, in such expressions as "vitello alla parmigianA" or the film "Divorzio all'ItalianA"? Style, in Italian, lo stile, is masculine. Maybe we could say the translation really is in the fashion (moda) of?
We use the feminine form of adjectives in such expressions because they stand for "alla maniera". In your examples,
- "alla parmigiana" = "alla maniera parmigiana",
- "all'italiana" = "alla maniera italiana".
In this Wikipedia article you can find an example of use of the expression "alla maniera italiana".