Re: marriages to non-pakistanis
Yep SGC it is a beautiful thing. We're all one human race after all. If everyone joined in, in a couple of generations we'd all be one big happy family!
As for kids and more than one language, I grew up speaking urdu as a second language with no problems. I did struggle in the urdu exams at school, but then so did all my urdu speaking pals since what you get taught in the syllabus is usually way too fancy compared to what you speak day to day!
A linguist once told me a bi-lingual/tri-lingual child appears to talk less, but this is not true. Let's say they're 1.5 years and starting to talk. Their peers speak 100 words a day, and you may get the impression that your child speaks half that. But the truth is they will be keeping up with their peers, only they'll speak 50 english words and 50 spanish words (example). So in fact, they too are saying 100 words a day like their peers.
Bringing up a child with more than one language has no negative effects on them.