(g) Serving a Minor or an Incompetent Person. A minor or an incompetent person in a judicial district of the United States must be served by following state law for serving a summons or like process on such a defendant in an action brought in the courts of general jurisdiction of the state where service is made.  

    A minor or an incompetent person who is not within any judicial district of the United States must be served in the manner prescribed by Rule 4(f)(2)(A), (f)(2)(B), or (f)(3) .

Rule 4(f)(2)(A), (f)(2)(B), or (f)(3):

(f) Serving an Individual in a Foreign Country. Unless federal law provides otherwise, an individual–other than a minor, an incompetent person, or a person whose waiver has been filed– may be served at a place not within any judicial district of the United States:

(2) if there is no internationally agreed means, or if an international agreement allows but does not specify other means, by a method that is reasonably calculated to give notice:

(A) as prescribed by the foreign country’s law for service in that country in an action in its courts of general jurisdiction;

(B) as the foreign authority directs in response to aletter rogatory or letter of request; or

(3) by other means not prohibited by international agreement, as the court orders.

 

Definition of ROGATORY LETTER aka LETTER OF REQUEST:

“1. A document issued by one court to a foreign court, requesting that the foreign court 1.) take evidence from a specific person within the foreign jurisdiction or serve process on an individual or corporation within the foreign jurisdiction & 2.) return the testimony or proof of service for use in a pending case. — Also termed letter rogatory; rogatory letter; requisitory letter. 2. An instrument by which an inferior court withdraws or waives jurisdiction so that a matter can be heard in the court immediately above. — Abbr. LOR.”