Do you speak English?
— Of \course I speak English.
Clearly this principle is not universal. If it \/were universal, | NNSs would not get it wrong when speaking English, as many of them certainly do.
In some languages the situation hardly arises, because freedom of word order allows non-foregrounded items to be placed away from the end of the utterance (if that is where the intonation nucleus normally goes, as it usually does). Or you rephrase the sentence so as to avoid repeating words.
When listening to non-Germanic foreign languages I always try to watch out for examples or counterexamples. (For Spanish, Héctor Ortiz-Lira has listed plenty of them in his articles on the subject.) But this can be difficult to do in the middle of a conversation when one’s knowledge of the language in question is limited.
The other day I called in at a printshop here in London to order some work. The assistant I dealt with gave me his business card. I saw that his name was obviously Greek, so I asked him
Μιλάτ’ ελληνικά; miˈlateliniˈka ‘Do you speak Greek?’—to which he replied
Βεβαίως μιλώ ελληνικά. veˈveozmiˌloeliniˌka ‘Certainly I speak Greek’.At least, I think that’s the accentuation he used. But I could be wrong. I’m not sufficiently au fait with spoken Modern Greek intonation to be certain of having heard the tonicity correctly. Did he really remove the accents from the last two words?
With Germanic languages there seems to be no uncertainty: they follow the English rule.
Sprechen Sie deutsch?
—Ja, natürlich spreche ich deutsch.
What about Romance languages? And other languages?
Vous parlez français?
—Mais oui, bien sûr que je parle français. (tonicity?)
Czy Pan mówi po polsku?