In words

InWords.php

<?php

class InWords
{
    private static $words = array();
    protected static $numbers = ['zero', 'jeden', 'dwa', 'trzy', 'cztery', 'pięć', 'sześć', 'siedem', 'osiem', 'dziewięć'];
    protected static $operands = ['+' => 'plus', '-' => 'minus', '*' => 'razy'];

    public static function get($str)
    {
        $s = explode(' ', $str);

        for($i = 0; $i < count($s); $i++)
        {
            if (is_numeric($s[$i])) {
                self::$words[] = self::$numbers[$s[$i]];
            } else {
                self::$words[] = self::$operands[$s[$i]];
            }
        }

        return implode(' ', self::$words);
    }
}