Most if not all United States courts apply what is called the "touch base" test when assessing privilege claims for foreign communications (to or from the U.S., or even totally overseas). That standard normally results in U.S. privilege law applying to a communication to or from the United States, or even to a purely overseas communication that relates to a United States matter. In the latter scenario, the "touch base" test is similar to the Second Restatement domestic choice of law analysis.
In In re Polygon Global Partners LLP, No. 21-mc-007 WES, 2022 U.S. Dist. LEXIS 6439 (D.R.I. Jan. 12, 2022), the court found it unnecessary to undertake a "touch base" analysis to determine whether U.S., Spanish or English privilege law applied to foreign communications. The court first explained "that the U.S. attorney-client privilege is more narrow than its English and Spanish analogues." Id. at *7. That meant that documents deserving privilege protection under United States privilege law "would also be shielded under the more protective foreign privileges of English and Spanish Law." Id. at *8. The court thus found it unnecessary to wrestle with "a number of declarations from a range of purported legal experts on Spanish law, many of whom offer inconsistent analyses of Spanish laws and doctrines." Id. at *9 (quoting In re Polygon Global Partners LLP, No. 21 Misc. 364 (ER), 2021 U.S. Dist. LEXIS 209512, at *19-20 (S.D.N.Y. Oct. 29, 2021)).
Some courts are lucky enough to avoid the difficult task of sorting out foreign privilege law.