Hello ! When you add an ISBN with the source button, it adds an oclc number for Worldcat (this is ok); but in addition, it automatically adds a "read online" link whereas the book is not available online. (See this discussion here in French). ~~~~
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The "read online" link is the French Wikipedia's standard URL parameter. The English Wikipedia (for example) puts the URL under the book title; the French Wikipedia adds the URL at the end of the citation instead.