At the time of this writing, Go does not yet have support for
internationalized locales for dates, if you create a month.yaml in your data/
folder with a content like shown below. It will work.

1: "janvier"
2: "février"
3: "mars"
4: "avril"
5: "mai"
6: "juin"
7: "juillet"
8: "août"
9: "septembre"
10: "octobre"
11: "novembre"
12: "décembre"

We assume PNG MIME type, because, from my understanding, PNG is the main format
for favicons nowadays (even if they have an "ico" extension). Further
configuration options are needed to allow for specifying different MIME types.