About legality on self-plagiarism when publishing an article I found out that a collegue published about 5 years ago a paper in the proceedings of a conference about education in engineering (proceedings has ISBN, but publication has no DOI, in case that matters for this question). Then reworded the whole paper but kept literally the same references, same research questions, same arguments all over the paper and published in another conference (IEEE, this time with a DOI). So I imagine he purposely reworded and made up two papers with "the same" content, though he obviously rewords paragraph by paragraph (changes sentence order, synonyms, etc.). I thought this practice was not allowed but does anyone know the legality of publishing the same paper (though reworded) in two conferences?
I don't know of any legal regimen in which self plagiarism is an issue. It is scientific misconduct, but not illegal, to use your own words and ideas without citing them. This is a case in which the legal and the ethical aren't the same. 

It isn't "stealing" ideas when you self plagiarize. It is just sloppy scholarship that makes it harder for readers and other scholars to find the complete context of the ideas expressed. 

Of course, if you have given up copyright to some words, then using those words again may violate the copyright that you once held, but no longer do. A publisher that holds the copyright might make a legal claim against you, but it isn't because of self-plagiarism, but copyright violation.