numbers => [null, eins/ein, zwei, drei, vier, fünf, sechs, sieben, acht, neun,
    zehn, elf, zwölf, 16 => sechzehn, 17 => siebzehn,
    20 => zwanzig, 30 => dreißig, 40 => vierzig, 60 => sechzig, 70 => siebzig
]
rules => [
    50,80,90 => {digit}zig,
    13-15,18,19 => {digit}zehn,
    21-99 => {digit}und{ten},
    100,200,300,400,500,600,700,800,900 => {digit}hundert
]
exponents => [
    singular => [tausend, Million,   Milliarde,  Billion],
    plural   => [tausend, Millionen, Milliarden, Billionen]
]
separator => ''