Complex sentence: Irish workers can communicate effectively with Americans--especially compared to those in other low-wage, non-English-speaking EU nations, such as Portugal and Spain; this factor was vital to U.S. companies' choosing Ireland for their European headquarters.
Split into simpler sentences: Irish workers can communicate effectively with Americans--especially compared to other low-wage EU nations such as Portugal and Spain. This factor was vital to U.S. companies choosing Ireland for their European headquarters.