Most of my extensions, especially the ones written in or after 2010 are released into the public domain.
For extensions that I've contributed to, assume that my contributions are licensed under the license that the extension is, or alternatively, assume they are released into the public domain. Whatever works for you and is legally OK; I'm not a lawyer.
I also translate interface messages into Finnish (fi), so if you need a Finnish translation for your extension, just ask me!
List of extensions that I've written (14) 
List of extensions I've contributed to (35) 
I've contributed to many extensions, this is merely a list of the extensions where my name is in the extension's $wgExtensionCredits
but I haven't originally written the extension in question. Social tools
in this listing.