This is my first name. I always thought it was a made up name, unique in its own way. To know it's very prevalent in other countries is kind of a let down but that's okay. I didn't like the name "Jan"... It just sounded and looked incomplete. Wouldn't change how it's spelled.
Janne is also a Dutch and Frisian given name. In both usages, the name is chiefly feminine, but it is also encountered on males (obviously to a lesser extent).In both Dutch and Frisian, the name is ultimately derived from Johannes (for males) and Johanna (for females). As a feminine name, one could also see the name as a variant of Janna or even as a short form of Janneke, which are both names that are in use in Dutch and Frisian and are virtually exclusively feminine. In rare cases, the name can also be a short form of Marianne, which is also found spelled as Marjan and Marjanne.Last but not least, the name is pronounced as YAHN-nə in both Dutch and Frisian.- http://www.meertens.knaw.nl/nvb/naam/is/Janne (in Dutch) - see page 70 of the book "Fryske foarnammen / Friese voornamen" written by Rienk de Haan (covers West Frisian given names and only lists the name as feminine) - see page 191 of "Friesche Naamlijst (Onomasticon Frisicum)" written by Johan Winkler (in 1898): http://images.tresoar.nl/wumkes/pdf/WinklerJ_FriescheNaamlijst.pdf (in somewhat archaic Dutch) and http://www.wumkes.nl/index.php?volg=8&id=95 (in Dutch; click on the red-coloured word "document" in order to download the PDF-file). This source also deals with West Frisian given names but lists the name as masculine instead. - "Rufnamen auf den Inseln Föhr, Amrum und Sylt von ca. 1600 bis 1900" (männlich): http://www.amtfa.de/friesVornm.pdf (in German; covers North Frisian given names and the name is listed as masculine here) - https://nl.linkedin.com/pub/dir/Janne/+/nl-0-Nederland (lists only bearers living in the Netherlands).
https://en.wiktionary.org/wiki/Janne#Estonian [noted -ed]