Many carriers in English speaking countries, including FedEx and UPS, require the full address - including the full country name - appear in English characters. You can sometimes use a foreign language address on the label if the names of the city, province, and country are also displayed in English.
However, character sets like Japanese, Chinese, and Cyrillic are often not supported by the carrier's label API, resulting in ??? symbols where the characters should be.
In such cases, the best option is to translate the address into English (by either emailing the customer or using a program like Google translate) and then edit the order's address in ShipStation to the English translation.
If you'd like to include the original address on the parcel, copy the original address to a program like Notepad, print it separately and tape it to the package next to the translated shipping label printed by ShipStation.
This is usually the best way to ensure that the address is both legible within the US as well as in the destination country.