How do we know if food is plural or not here?
You don't really need to know. Although some people would say 'local foods' in English, food is both a singular and plural form, so to say "I like all the different local food." is totally correct.
Good too know
I thought adjectives took the e-form is they came before a noun - at least that's what another post says.
They do when preceded by a definite article – eg. den smukke by.
They don't when preceded by an indefinite article – eg. en smuk by.
I like local food too.Might we be friends?