Problem with January

I'm currently developing a french style for our department, and we happen to speak french over here ;)

My Firefox locale is set to "Fr-fr", same for the style as well, every french constant seems to work fine as far as I can see except for the month of... January.

If i specify numerically (or textually - without accents) every other month in the date field of an item, it gets rendered as the correct french name, except for january, which displays nothing at all.

Bug? Or something on my side?
Thanks!
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