How to reproduce (using Firefox 59.0.2 (64-bit) on Ubuntu 16.04):

• on Wikidata, search for an item with a query containing a simple quote ('), for instance foofoo ' barbar
• on the search results page, when there is no result, the UI provides a link to create the item with the query as label; click on the link
• on the page loaded after the click on the link, the form is filled with a label that is too much escaped, with an HTML entity displayed: foofoo ' barbar

Workaround: the user can (and need to) edit the label before creating the item.