As a third-party tool, it can potentially cause system instability or issues. Steps to Use Vistalizator

Note that using Vistalizator to install restricted language packs may break the Windows End User License Agreement (EULA).

Overrides the one-language limit on non-Ultimate editions of Windows 7 and Vista.

If you experience a "black screen of death" (KSOD) after using it, try using the "Last known good configuration" in the boot menu (F8).