As I learned other languages I realized that some phonemes which are common in one language are not so familiar in others. There are even cases where some phonemes do not exist in other specific languages.
Keeping that in mind, how can I teach someone, who's learning a new language to pronounce those previously unknown phonemes? I know there is the International Phonetic Alphabet (IPA), but it is not widely known by the general public. Suppose this new language learner is not aware of the IPA.
If that question seems a bit vague, let's be more specific. How can I teach someone who only speaks German to say the French J (like in je, or jaune)? Or how can I teach a Spanish speaker to pronounce the Portuguese ão (like in mão or avião)?