Can papers that have been published in a journal be presented by the author in an International conferences? Are there any restrictions or permissions needed from the journal publishers?
No, because the journal has the copyright. You would have to get permission from the editor of the journal, and admit to the conference organisers that this paper had already been published. But then nobody will want to come to the conference, because they can read your paper at home!
So, think carefully about sending a paper to a journal if you wish to travel to get feedback!
However, you could present an updated version, or on e with a different focus of analysis.
It is the words of the paper that are copyrighted, not the ideas. Still, the assumption is that every publication and presentation has something that makes it different from previous publications and conferences.