Islam is a religion not a race or nationality so I assume you are asking about a Muslim marrying a non-Muslim rather than a foreigner.
After all, you do get Muslims and non-Muslims in the same country, so it wouldn't necessarily mean marrying a foreigner to marry someone of a different faith. Likewise, a Muslim from one country could marry a Muslim from another country.
It can cause a lot of difficulties when two people of different faiths marry. However, there are a number of successful 'mixed' marriages and relationships. I think the success or otherwise is mainly down to the two people involved but outside factors will also have an effect. The attitude of their families and community can either help or add a lot of pressure.