If live in the US and you have a Twitter account, your data is stored on servers within the U.S. so that NSA can access all your data. However, if you live anyplace outside the U.S., your Twitter data is stored in Dublin, Ireland, so that NSA cannot access your private information.
The changes will be complete by 18 May 2015 and Twitter briefly explains them in a policy update post:
“If you live outside the United States, our services are now provided to you by Twitter International Company, our company based in Dublin, Ireland. Twitter International Company will be responsible for handling your account information under Irish privacy and data protection law, which is based on the European Union’s Data Protection Directive.
“If you live in the United States, the services will continue to be provided to you by Twitter, Inc., based in San Francisco, California, under United States law.”
Details may be found on Twitter at https://support.twitter.com/articles/20172527.