Update 13 July 2020 see for an illustration of the issues, Matthians Lehmann here, on the classification by German judges of the mahr, akin to a dowry – with consideration (and eventually side-stepping of all) of the Rome I, III, and the maintenance and matriomonial property Regulations. The Court’s analysis feels like ten little monkeys bouncing on a bed: one by one the Rome I, Maintenance, Matrimonial property, Rome III Regulations are considered yet cast aside. See also Jan Jakob Bornheim’s reference here to Almarzooqi v Salih,  NZHC 1049, where the New Zealand High Court assumed that the mahr was a contractual promise without much consideration of the characterisation issue. And Mukarrum Ahmed, who commented ‘in England, the leading case on the characterisation of mahr is Shahnaz v Rizwan. The wife’s claim was treated as a contractual obligation.’ [GAVC, that’s Shahnaz v Rizwan  1 QB 390].
Anyone planning a conflict of laws course in the next term might well consider the succinct Council of Europe report on the application of islamic law in the context of the European Convention on Human Rights – particularly the case-law of the Court. It discusses ia kafala, recognition of marriage, minimum age to marry, and the attitude towards Shari’a as a legal and political system.
Needless to say, ordre public features, as does the foundation of conflict of laws: respect for each others’ cultures.