When using Dopus to zip files containing the character ø or Ø in the filename, the zipped filename is not correct. The 'ø' becomes 'o' and 'Ø' an 'O'.
Works fine for me. Checked in Opus and 7-Zip.
Are you looking at the zip file in Opus, or in something else? If it's something else, are you sure it supports Unicode zip files? Not all software does (although most does these days.)
If you are editing an existing archive that was made by something else, Opus won't add Unicode names to an archive that wasn't created with them enabled. But you can extract the archive and create a new one from the contents to work around that. Adding files to the new one will then be fine.
(There are also some archives made by some software, mostly old software, where the main names in the archive are not Unicode but an extension is used to store alternative Unicode names for each file. That kind of archive is quite rare, and Opus only reads the main names. If you extract and re-create those using e.g. 7-Zip, they'll work fine in Opus.).
My Windows 8.1 version is in English with Danish keyboard, and the problem reminds me of the troublesome DOS world with the Nordic æøå characters, where ø was not included in the standard codepage, and had to select the Nordic 865 codepage.
Have included 1 Opus and 2 WinRAR files
Creating the Dopus zip file was done in the Opus Context Menu by right clicking the created "æøå-ÆØÅ.txt" file and select Add to in the Directory Opus Archives submenu.
The RAR files were created the same way using Opus WinRAR submenu.
I am sure it has something to do with Opus, as I have not experienced this in any other Windows application.
Dopus - øØ.rar (576 Bytes)
Which language do you have set here in Control Panel? I'll try using the same and see if I can reproduce what you're seeing.
Here is my Windows 8.1 Region setup.
If I change the 'non-Unicode' setting to Danish, Opus zipping is working correct so Unicode for the filenames is not used.
As shown WinRAR is working correct on this issue.
Are you sure you used the Opus "Add to Zip" and not another context menu entry (e.g. not Send to -> Compressed folder)?
I've reproduced what you were seeing. Using English (United States) as the codepage was the key. (That character must be in the UK English codepage but not the US English one.)
I've done a fix for this that will be in the next update.