This class does not affect compression, it's just used to encode and decode entry names and comments. The initial version of ZIP format did not support UTF-8. So, some old zip utilities might not recognise this format. Change Encoding property to some other value if you need backward compatibility. Note that Encoding.Default seems like a logical choice but doesn't really work for international locales. Instead, we need to create an encoding using the current OEMCodePage. That allows accents and international characters to be used in file names (like the zip built into Windows, allows names such as "Åland.txt", "Äiti.txt", "Würth.txt", etc.).

Reference

ZipEncoding Members
C1.C1Zip Namespace