Do aircraft technicians need additional certifications to work in other countries?
I don't have personal experience, but this is absolutely something you can do. 

Unfortunately many countries do not have the exact same standards or licensing scheme, so often your licence is not automatically converted, but you rarely need to start from scratch. 

For example, if you wanted to come to Australia, you would need to attend a CASA approved Part 147 training organisation, which are located around the world. They will assess you, possibly provide you with some extra training, following which you can apply for an Australian Part 66 engineer licence. Once you get that licence you shouldn't have too much difficulty migrating, but that's a discussion outside of my league. More details on this conversion process are on the CASA website.