I have a thread title: "porównanie monitorów odsłuchowych"
which appears in the URL as "por-wnanie-monitor-w-ods-uchowych".
In Xenforo the same topic appears as "porownanie-monitorow-odsluchowych".
As you see above, language specific accented characters are automatically converted to their root originals, specifically in this example: ó > o and ł > l.