Validating international phone numbers using regular expressions in Java can be a bit more complex than validating North American phone numbers, due to the wide variety of formats used around the world. Here is an example of a regular expression pattern that can be used to validate international phone numbers:

String phonePattern = "^(?:\\+\\d{1,3}(?:[\\-\\.\\s]\\d{1,3}){1,3}|0(?:[\\-\\.\\s]\\d{1,3}){1,4}|\\(\\d{1,3}\\)(?:[\\-\\.\\s]\\d{1,3}){1,3})$";

This regular expression pattern matches phone numbers in several formats, including numbers with a country code and numbers without a country code. The "+" symbol indicates the beginning of a phone number with a country code, followed by up to three digits for the country code. The rest of the phone number can be separated by a dash, a period, or a space, and can consist of up to three digits at a time.

To use this regular expression to validate an international phone number, you can use the following code:

String phoneNumber = "+44 20 1234 5678";
if (phoneNumber.matches(phonePattern)) {
    System.out.println("Valid phone number: " + phoneNumber);
} else {
    System.out.println("Invalid phone number: " + phoneNumber);
}

In the example above, the "phoneNumber" string is checked if it matches the "phonePattern" regular expression. If it does, it is considered a valid phone number.

Note that while this regular expression pattern is a good starting point for validating international phone numbers, it may not catch all invalid phone numbers. It's always a good idea to double-check any phone numbers entered by a user, and to use additional validation methods (such as sending an SMS verification code) to ensure the number is valid.