Complex sentence: Mellel has a unique way to handle footnotes, endnotes and comments; they are treated as different streams of a single text which can also help to keep different translations of the same text in sync.
Split into simpler sentences: Mellel has a distinctive way of handling footnotes, endnotes and comments, which are treated as different "streams" of a single text. This feature can also help keep different translations of the same text in sync.