French month May 'mai' is not recognized by setLanguage.

[HistoireDeBabar]

Example:
Date.i18n.setLanguage('fr-FR');
var date = Date.parse('20 mai 2015');

The month attribute of date defaults to the current month when parsed.

[regevbr]

this happens in other languages as well.
The cause seems to be that the normalizer first replaces all month names to english, before parsing the string. Then, the translated month is being captured by other regex that mistakenly translate it.
The fix is to remove the month names normalization.
You can see fix in my fork - https://github.com/regevbr/datejs/tree/v1.0.0-rc4