IsVowel

public static class CharExtension
{
    public static bool IsVowel(this char ch)
    {
        return "aeiouyáéíóúýa̋e̋i̋őűàèìòùỳầềồḕṑǜừằȁȅȉȍȕăĕĭŏŭy̆ắằẳẵặḝȃȇȋȏȗǎěǐǒǔy̌a̧ȩə̧ɛ̧i̧ɨ̧o̧u̧âêîôûŷḙṷẩểổấếốẫễỗậệộäëïöüÿṳḯǘǚṏǟȫǖṻȧėıȯẏǡạẹịọụỵậȩ̇ǡȱảẻỉỏủỷơướứờừởửỡữợựāǣēīōūȳḗṓȭǭąęįǫųy̨åi̊ůḁǻą̊ãẽĩõũỹаэыуояеёюийⱥɇɨøɵꝋʉᵿɏөӫұɨαεηιοωυάέήίόώύὰὲὴὶὸὼὺἀἐἠἰὀὠὐἁἑἡἱὁὡὑᾶῆῖῶῦἆἦἶὦὖἇἧἷὧὗᾳῃῳᾷῇῷᾴῄῴᾲῂῲᾀᾐᾠᾁᾑᾡᾆᾖᾦᾇᾗᾧϊϋΐΰῒῢῗῧἅἕἥἵὅὥὕἄἔἤἴὄὤὔἂἒἢἲὂὢὒἃἓἣἳὃὣὓᾅᾕᾥᾄᾔᾤᾂᾒᾢᾃᾓᾣæɯɪʏʊøɘɤəɛœɜɞʌɔɐɶɑɒιυ"
                 .Contains(""+ch);
    }
}

'x'.IsVowel() == false
'a'.IsVowel() == true
'ö'.IsVowel() == true
'č'.IsVowel() == false
'ᾃ'.IsVowel() == true