Choshen Mishpat 348. No, You Can’t Seize the Property of a Non-Jew
The Quote
“All property of other nations belongs to the Jewish nation, which, consequently, is entitled to seize upon it without any scruples.” — Schulchan Aruch, Choszen Hamiszpat 348:
The Reality
The Shulchan Aruch (of which Choshen Mishpat is a part) is not a part of the Talmud but a later work, composed in the 1500s.
In any event, the quoted text does not appear in chapter 348 of Choshen Mishpat (or anywhere else).
Chapter 348 of Choshen Mishpat deals with laws concerning theft. The text of Choshen Mishpat 348:2, in fact, says the exact opposite of the quote’s claim.
Choshen Mishpat 348:2 states:
Anyone who steals even the equivalent of a perutah [the least valuable coin] violates the prohibition of “Do not steal” [Leviticus 19:11] and is required to repay, whether one steals money from a Jew or money from a non-Jew or from an adult or a child.”
(sections in my brackets are mine, to explain terminology and sources)
Clearly, theft from non-Jews is forbidden according to the text of the Shulchan Aruch, and if it is done illegally, the stolen amount must be repaid to the non-Jew.
Summary:
A fake quote that does not exist. The text of the chapter makes the opposite point, that it is forbidden by Biblical law to steal from a Jew or non-Jew and that anyone who does so is required to repay the theft.