It would share most characters in common, but assign other locally useful characters to several code points reserved for "national use".
ɪt wʊd ʃˈɛɹ mˈoʊst kˈæɹɪktɚz ɪn kˈɑːmən, bˌʌt ɐsˈaɪn ˈʌðɚ lˈoʊkəli jˈuːsfəl kˈæɹɪktɚz tə sˈɛvɹəl kˈoʊd pˈɔɪnts ɹɪzˈɜːvd fɔːɹ "nˈæʃənəl jˈuːs".