In fact, the fertility rate in Turkey is now pretty close to the reproduction rate: 2.21 according to the 2009 estimate of the CIA's World Factbook, and 2.2 in 2006 according to Turkstat. (In the second link, annual data from 1990 shows the decline in this and the growth rate nicely.)

As for the wider Muslim world, a nice graph from a German article on the subject:

As for Muslims in Germany,

(From top to bottom: Turkish women in Turkey, Turkish women in Germany, German [women], German Muslim women.)

Now that was demographics. As for secularisation, with focus on Turkish immigrants to Germany, I summed up results of a few studies in this comment on ET (in 2005).

_{*Lunatic*, n.
One whose delusions are out of fashion.}