What is Buddhist law of marriage ? Is there any? Should both partners be Buddhist in a marriage?
If they want get a love marriage can they still get married if one of the partners is not Buddhist. What is the law in Buddhism about marriage?
There is no such as a Buddhist law on marriage. If you like to have a long time partner its always good to have the same tendencies as he/she but such is not merely up to religion. Virtue, generosity, gratitude... all this things are not limited to a certain religion. So to seek for a partner with equal virtue or virtues one likes to follow, is quite good.

And there is no such as any cultural, national, or what ever discrimination. Of course such plays, even so, always a rule in live and society as much traditions have also to do with common virtues. The world is not full of Arahants and Noble Ones.

(thoughts come up sometimes ...and now they like to be great yogis ...  :-)  "I wan it all", but not to speak about those who even do not take on the responsibility of partnership)