Sale, you still not see your Opera entry in the Applications menu?
Mojo tried your .desktop file, and it's Ok on his system.
I tried to install your package, and it's Ok on my system, I have menu entry, and Opera browser works as expected.
Ok. Reading Desktop Spec and let's think, how we can hide menu entry.
First, as already mentioned above — is to set both categories at a time: "System" and "Settings"
If you see it, please, delete one of "System" or "Settings". It's bug of current SliTaz menu. I've fixed it, but we need to wait, when new package is synced with Mirror, then anyone will can upgrade package "slitaz-menus".
Next, touch Desktop Spec http://www.freedesktop.org/wiki/Specifications/desktop-entry-spec
Remove any lines started with OnlyShownIn, if you want to show your menu entry in any desktop environments.
True or On or 1 or etc. — remove this line.
Also, true or on or 1 or etc. — remove this line.
Remove this line. If menu can't find applicationName, then it hide it menu entry.
If you checked your .desktop file in the /usr/share/applications/, and it's seems Ok, and desktop-file-validate says Ok, but you see not results in the menu, try next —check your user's folder /home/user/.local/share/applications
User's Application menu is merged from system-wide .desktop files and user-specific .desktop files.
You see no Opera? Check, do you have any Opera-specific .desktop files in that folder?
You can have system-wide Opera .desktop file for all users in your machine.
And you can have same Opera .desktop file in /home/user/.local/share/applications with little modification — your user (you) can hide this menu entry using "OnlyShowIn", "NoDisplay", "Hidden" or "TryExec" as mentioned above.
And, finally, check your
User's Application menu layout merged with menu files found in these folders. These folders are empty by default, and empty on my user's home folder.
Also, root user can have all that "pitfalls", in little addition — root's home folder is just /root, not /home/root.