Within 6 months of filing a foreign trademark application, it is possible to use that application as a basis for filing a U.S. application.
An advantage to using a foreign trademark application as the filing basis for a U.S. application is that you do not have to show use in commerce within the U.S. to secure your initial registration. Although, you will have to show use of the mark in commerce within the United States when the mark is renewed between the 5th and 6th year after the date of U.S. registration.
Note that your U.S. application needs to be identical to your foreign application and cover the same trademark and the same goods and services.
For example, if your foreign application is for a logo, then your U.S. application needs to cover the same, identical logo. Further, the international classes and the listing of goods and services on your foreign application will need to be copied over to your U.S. application. You can not add goods and services to your U.S. application that are not listed in your foreign application and claim your foreign application as the filing basis for those new goods and services. However, if you only want to protect some of the classes listed in your foreign application, and not all of them, that is permissible.
To finalize your U.S. application that is filed based on a foreign registration, we will need to provide the U.S. trademark examiner a copy of the foreign registration, translated into English. At that time, the foreign registration is reviewed to ensure that the international classes and goods and services match the U.S. application before a registration will issue.
It is important to note that having a foreign application or registration does not guarantee that a registration in the U.S. will issue for your mark. Every application, regardless of the filing basis, is reviewed for compliance with U.S. trademark law and for confusing similarity with earlier filed and registered U.S. trademarks.