I think the romans were quite pragmatic in their romanisation.... Those people that saw the benefits of the roman system and had abilities were integrated into the bureaucracy and/or military.... Ethnically the roman empire was very diverse. Also local traditions were kept in place by the romans if they did not hinder them....

I'd like to add one other thing. quite a few people on here seem to visualize the roman empire as a modern Nation State, and I think that is wrong. The idea of a nation state, is quite new and only started to gain ground in the 19th century. The definition of a nation state as taught in history is that it's a territorial entity whose inhabitants feel connected through language and culture. Following this definition one might even argue that a lot of modern states in Africa and Asia are not nation states at all.... Now Latin quickly became the langua franca (quite obvious) but culturally the empire was very diverse. It's only to easy to look at the roman empire in the context of the world today, but I don't think that's very useful. Just some food for thought