We say ‘fourteen’ but not ‘four and ten’. Fourteen comes out as one word, like eleven. If ‘fiveforty’ were a word it would be easier to process as one word instead of five and forty which tends to be processed as two words.
Vierzehn and Vierundfünfzig are single words in German, but separate words in English. "Fourteen" (four and ten) being a single word is actually strange in English because the language normally splits words like these.
English has decided to use single words up to 20. Other European languages stop at 100. Both are arbitrary and right or wrong in their own way.
The English word would be "five and forty" because "fiveforty" would probably mean 200 going by traditional English (in the same say "four score and seven" means 4*20+7, not 24+7).
