If you're asking how to practice immigration law in other countries then it will very much depend on the country. It will also depend on if you've already received a law degree in the US and if you'll be helping people immigrate to the US or into that country.
I would start by looking into what it would take to work in the country that you're interested in. Depending on what law you want to practice, you may want to obtain your law degree in that country.
If you are thinking of practicing immigration law with a focus on a particular community from a certain country, a good idea would be to become familiar with the cultural liaisons of that country -- the embassy or consulate, for example; groups and associations that focus on this community, etc. Also always a good idea to have a good network of other immigration attorneys who could direct you to clients of that group.