Consider Polish. It's a language with an ethnic basis and a political basis. Poles in Poland speak it. So do some others, such as goulo. Not hard to see why Polish might be characterized as a "foreign" language, from an American point of view.
What about languages which have lost their ethnic and political basis, but remain in use? I'm thinking here of liturgical languages such as Latin or Old Church Slavonic. They don't have cradle speakers, but there is a reasonable population of adult speakers who perpetuate the language. How are they foreign? There hasn't been a Latium in a very long time.
Likewise invented languages. Esperanto has very few cradle speakers, but there is certainly a healthy community of adult speakers. And while Esperanto has a political slant, it is not a state language anywhere. Quite deliberately so.
Then there are languages with an ethnic basis but no current or historical political basis. Romany, or Yiddish. Likewise dead languages, such as Sumerian or Tocharian A. No speakers, no ethnic affiliation, no political basis. But they are still studied to a limited degree. (Distinguish this from Attic Greek, which has a descendant culture that claims affiliation with its ancient form.)
The most ridiculous example of a "foreign" language would an indigenous tongue. Cherokee or Iroquois can't possibly be foreign here in North America. English is the invasive species. If you're looking at the question from the British Isles, likewise Manx and Cornish.
Clearly this isn't a serious issue. One very common usage of "Foreign" just means "not local", as in "foreign food," "foreign parts", and the phrase "this was foreign to me". "Foreign language" means the language we don't speak here. I just find myself wondering how much the conceptual freight of the word "foreign", with its connotations around patriotism and political power, imbues the way people think about non-English languages. Would the English only movement be so attractive to some people?
One irony of the barely-disguised racism and anti-immigrant sentiment of the English only movement is that English as we know and love it is a Romance-Germanic creole of Norman French and Old English. Driven underground for generations by an overwhelming military conquest and subsequent permanent occupation, our own language was what the field hands and kitchen help spoke, while the people with money and status and power conversed in French. Our linguistic ancestors, and in my case genetic ancestors, were marginalized, overwhelmed and discriminated against, because English was a foreign language in its own country.