On Wikimedia wikis, local uploading should be disabled if there are no licenses set on MediaWiki:Licenses.
The need for this is because some or many small WMF wikis still do not have
license options, which is really needed for our copyright requirements.
This will be done in https://gerrit.wikimedia.org/r/#/c/136520/
After this change, simply putting any content on MediaWiki:Licenses will enable uploading again.
I developed a tool at https://tools.wmflabs.org/robin/?tool=uploadconfig which provides information about the status of each wiki.