We can think of (often confused in the public minds) P (which suggest the need for) Q (two factors) R (an international language) S The correct sequence should be

Since, the sentence starts talking about the thought process, R will be the next statement as it is talking about the two factors. Q will be the continuing statement as it carries a relative pronoun which connects both the statement. S follows Q as it discusses the need for a language and P discusses why there is a need for the international language.

The correct formation would be, ‘We can think of two factors which suggest the need for an international language often confused in the public mind’.