°µÍø½ûÇø

Getting married in Germany as a foreigner is very difficult: You need a lot of paperwork done, many official translations (which cost money) and need to be very patient - my friends needed 6 months (and several thousand Euros) until they finally could marry!
That's why many foreigners get married elsewhere (e.g. Denmark) and have it recognised in Germany afterwards, which is easier.
But your question was about marrying on a tourist visa: Yes, as far as I know this is possible. But the tourist visa CANNOT be converted to residency! So you would have to return to your home country after the wedding and apply for a family reunion visa from there.

According to the latest information that I have there are presently only 13 nations where same-sex marriage is legal and Germany is not one of them, so until that changes you would most likely not be able to obtain permanent residency based on marriage anyway.

Countries where same-sex marriage is recognized as legal:

Netherlands - since 2000
Belgium - since 2003
Canada - since 2005
Spain - since 2005
South Africa - since 2006
Sweden - since 2009
Norway - since 2009
Iceland - since 2010
Portugal - since 2010
Argentina - since 2010
Denmark - since 2012
France - since 2013
Brazil - since 2013

Same-sex marriages are partially legal in Mexico and the United States of America. The UK is moving towards legalization. The Australian High Court has recently overturned the ACT same-sex marriage law so presently it is no longer legal in that nation.

Cheers,
William James Woodward, °µÍø½ûÇø-blog Experts Team

Oh, sorry, I really overlooked this small but very important detail, which was only mentioned in the subject line: SAME SEX MARRIAGE!
As WJ said above, those are unfortunately not recognised in Germany and you cannot get a visa based on one.