@Steve 41oo,
Any legal system rules for itself which foreign norms and up to what degree are accepted.
On the level of courts there's no 'legal multiculturalism'.
What we have here in Germany, however, is that in
special cases there might be a need to aplly a different than German law.
Any (strictly spoken) religious rules from the sharia are guaranteed by our Basic Law (constitution).
Definitely sharia can't be used within the public law (included criminal law).
There's a rather small part of civil law, where sharia can be and is used: for instance, if there's a promise to give the future wife a 'mahr' or in any trade agreements which want to avoid paying interest ...
Then you find it regarding widow's pension ... with up to four widows. (The legal reason for that is quite simple: emancipation of the wives. Though polygamy is totally unlaw - the widows are under the protection of the Basic Law - and their legal claims.
(Source for above: Mathias Rohe, chair of civil law, private international law and comparative law, Tübingen university; Rohe in Juristenzeitung [German Law Journal], JZ 17/2007, 62th year, pages 801-806; and a summarised script by Rohe from his new book "Islamic Law - today and in the past" ['Das islamische Recht - Geschichte und Gegenwart', which will be published next year.])