Caused by: org.xwiki.officeimporter.OfficeImporterException: Error while converting document [Tést Two.docx] into html.
Caused by: org.xwiki.officeimporter.converter.OfficeConverterException: Error while performing conversion.
Note that the same file, without the accent in the name works properly.
I managed to reproduce it on some servers running XWiki 6.4.8 and 5.4.6, with both office servers 3.6 and 4.1 (libre office).
On other servers it works fine, including a local install of XWiki 6.4.8 with libreoffice 3.6.
I also managed to reproduce the same scenario (documents with accents fail but without accents work) on a 8.4.4 as well, but with a different exception.