On New Year's Day, Bulgaria will achieve its decades-old goal of joining the euro currency union and deepening ties with the more prosperous countries of Western Europe. Membership is expected to promote cross-border trade and investment, and the Bulgarian government pressed for years to get in. Yet polls show the changeover is taking place against a background of widespread skepticism among ordinary people. Here are things to know as Bulgaria and its 6.4 million people become the 21st member of the Eur ...