Provided as a 1-function library, and a basic command-line utility (nbr — will certainly be renamed to something longer and less likely to name clash).

More advanced functionnalities could be added when needed. Here are some references:

https://leconjugueur.lefigaro.fr/frlesnombres.php
https://www.miakinen.net/vrac/nombres
https://www.dcode.fr/ecriture-nombre-lettres