Is this a true statement about localization support in IdentitylQ?

The statement isfalse. In SailPoint IdentityIQ, while message files may indeed be added to support additional languages, the out-of-the-box supplied message files can also be modified. Administrators can customize these message files to adapt the text in the user interface to better suit the organization’s needs. This includes modifying existing translations or adding custom messages to meet specific requirements.

References:

SailPoint IdentityIQ Localization Guide

SailPoint IdentityIQ Configuration Guide (Customization of Message Files)