xliff files with 2-letter language coding

Hi, I've many xliff files with 2-letter language coding:

<?xml version="1.0" encoding="utf-8" standalone="no"?><xliff xmlns="urn:oasis:names:tc:xliff:document:1.2" version="1.2"><file original="1-b6de1de89058fcb96bd8" source-language="it" target-language="en" datatype="plaintext"><header>....

When opening for translation, Studio says "The detected target language does not match that expected by the project".

How can set Studio to accept 2-letter code?