greeklish.php

function greeklish($string)
{
    $replace_pairs = [

        'Α' => 'A',
        'Ά' => 'A',
        'Β' => 'V',
        'Γ' => 'G',
        'Δ' => 'D',
        'Ε' => 'E',
        'Έ' => 'E',
        'Ζ' => 'Z',
        'Η' => 'I',
        'Ή' => 'I',
        'Θ' => 'Th',
        'Ι' => 'I',
        'Ί' => 'I',
        'Ϊ' => 'I',
        '΅Ι' => 'I',
        'Κ' => 'K',
        'Λ' => 'L',
        'Μ' => 'M',
        'Ν' => 'N',
        'Ξ' => 'Ks',
        'Ο' => 'O',
        'Ό' => 'O',
        'Π' => 'P',
        'Ρ' => 'R',
        'Σ' => 'S',
        'Τ' => 'T',
        'Υ' => 'Y',
        'Ύ' => 'Y',
        'Ϋ' => 'Y',
        '΅Υ' => 'Y',
        'Φ' => 'F',
        'Χ' => 'X',
        'Ψ' => 'Ps',
        'Ω' => 'O',
        'Ώ' => 'O',
        'α' => 'a',
        'ά' => 'a',
        'β' => 'v',
        'γ' => 'g',
        'δ' => 'd',
        'ε' => 'e',
        'έ' => 'e',
        'ζ' => 'z',
        'η' => 'i',
        'ή' => 'i',
        'θ' => 'th',
        'ι' => 'i',
        'ί' => 'i',
        'ϊ' => 'i',
        'ΐ' => 'i',
        'κ' => 'k',
        'λ' => 'l',
        'μ' => 'm',
        'ν' => 'n',
        'ξ' => 'ks',
        'ο' => 'o',
        'ό' => 'o',
        'π' => 'p', 
        'ρ' => 'r',
        'σ' => 's',
        'ς' => 's',
        'τ' => 't',
        'υ' => 'u',
        'ύ' => 'u',
        'ϋ' => 'u',
        'ΰ' => 'u',
        'φ' => 'f',
        'χ' => 'x',
        'ψ' => 'ps',
        'ω' => 'w',
        'ώ' => 'w'
    ];

    return strtr($string, $replace_pairs);
}