UploadWizard is a WIP, a "work in progress". It is functional and sometimes it breaks. Typically it breaks nicely; it may for instance not show the thumbnails and in some places it is incomplete; it does for instance not yet support RtL languages.
It is however at a stage where the developers want the software to get a hammering. One of the best indicators for this is that there is now software producing statistics for its use. One of the aspects they are looking for is the use in different languages.
To get people to use the UploadWizard in other languages, it needs to be localised. As always translatewiki.net is happy to welcome any new localisations including ones for the UploadWizard.
On Wednesday a new version of the UploadWizard is scheduled to go in production. This means that today's efforts will likely be available tomorrow. For many languages the localisation has already been completed. Please use Commons in your native language and tell us about your experience by providing feedback.