Daniel 2:4 to the end of Daniel 7 is written in Aramaic. Does the type of Aramaic used there support the view of the higher critics who assert that the book was composed in the second century BCE near the time of the persecution of Antiochus Epiphanes, and not in the sixth century BCE according to the traditional view? The classic commentators do not address this issue which has arisen in modern times, and the few modern Jewish commentaries on Daniel, if they do address it, are not available in English on the Internet.
The question posed requires an expert in Aramaic. One such expert was Sir Godfrey Rolles Driver. In 1926, in an article in Journal of Biblical Literature, Volume 45, 'The Aramaic of the Book of Daniel,' he demonstrated that the Aramaic of Daniel is certainly later than the Aramaic of the Elephantine Papyri, which date from the end of the fifth century BCE: https://www.jstor.org/stable/3260169.
Since G. R. Driver's study, fragments of Daniel were discovered among the Dead Sea Scrolls at Qumran. These finds challenge the view that the book was composed in the time of the Maccabees in the late second century BCE, but they do not overthrow Driver's linguistically established later-than-the-fifth-century BCE view. See Gerhard Hasel, 'New Light on the Book of Daniel from the Dead Sea Scrolls' (1992): http://www.biblearchaeology.org/post/2012/07/31/New-Light-on-the-Book-of-Daniel-from-the-Dead-Sea-Scrolls.aspx#Article
Klaus Koch in Das Buch Daniel (1980) has attempted more precision. He concluded that recent research (which he thoroughly documented) suggests that the Aramaic of Daniel is Imperial Aramaic which should be dated no later than 300 BCE. He boldly asserted that higher critics and their Maccabean date have lost the battle (pp. 45-46).
The Aramaic in the Book of Daniel has two purposes: (1) the Aramaic provided a perfect chiasm to the parallel Hebrew portions of the text; and (2) the Aramaic is special divine revelation to the Gentiles, who spoke Aramaic.
First, there are two chiasms in the Book of Daniel: one in Aramaic and one in Hebrew. Both sets of chiasms appear to be parallel in content and meaning notwithstanding they are not in chronological order (and therefore the chiasms were easier to construct). For example, the first chapter of the Book of Daniel is an introduction (Hebrew), however chapters 2-7 (Aramaic) and 8-12 (Hebrew) appear to be in precise chiasmic order: that is, chapters 2-7 (Aramaic) appear to be one chiasm and chapters 7-12 (Hebrew) appear to be the second parallel chiasm. Both chiasms appear to be precise parallels in content and meaning.
Chapter 1 - Introduction
Chapter 2 - Kingdom Rule (Four Gentile + 1 Jewish)
Chapter 3 - Tribulation & Testing from Gentile power
Chapter 4 - Divine deliverance by angel(s)
Chapter 5 - Divine deliverance by angel(s)
Chapter 6 - Tribulation & Testing from Gentile power
Chapter 7 - Kingdom Rule (Four Gentile + 1 Jewish)
As mentioned, chapters 2-7 are in Aramaic because the text indicates that the direct audience of the divine revelation were Gentile world rulers (Nebuchadnezzar and Belshazzar).
On the other hand, the audience for the remainder of the book appears to be Jewish because there are seven mentions of the sacred Tetragrammaton, which would only resonate with devout Jews. Also, there are several allusions to the fulfillment of the prophecies of Jeremiah, which would only resonate with devout Jews. The second chiasm repeats (and amplifies) the earlier chiasm of the book in content and meaning, which is common to the dichromatic structure of all Hebrew narrative and poetry.
Chapter 7 - Kingdom Rule (Four Gentile + 1 Jewish)
Chapter 8 - Tribulation & Testing from Gentile power
Chapter 9 - Divine intervention by angel(s)
Chapter 10 - Divine intervention by angel(s)
Chapter 11 - Tribulation & Testing from Gentile power
Chapter 12 - Kingdom Rule (Jewish)
Both chiasms describe events that are not in chronological order, because if the events were in chronological order, the chiasms would not work. For example, in the first chiasm the events of Chapter 7 occurred before the events of Chapter 5 (compare Dan 7:1 with Dan 5:30); and in the second chiasm the events of Chapter 10 occurred before the events of Chapter 9 (compare Dan 10:1 and Dan 9:1). This flipping and flopping of chronology therefore made the logical formation of the respective chiasms possible, because if the text reported the events in chronological sequence, the chiasms would have been fractured.
In summary, the Aramaic of this book was deliberate and had a twofold purpose: (1) the Aramaic provided a perfect chiasm to the parallel Hebrew portions of the text; and (2) the Aramaic was direct special divine revelation to the Gentiles, who spoke Aramaic. A third purpose now appears evident: the arrangement of Aramaic and Hebrew in chiasm was to preserve the text from later corruption. In other words, the brilliance of the Jewish author of this text was to write predictive prophecies in such a way that should later copyists corrupt the text, the chiasms would fracture. For example, the Septuagint, the Vulgate, and many other ancient and modern translations of the Book of Daniel contain corrupt deutero-canonical elements, because the Aramaic and Hebrew chiasms are fractured. In other words, the Book of Daniel was written and structured with the subtle, nay, almost undetectable nuance of chiasm which later copyists failed to notice when they sought to corrupt the text with extraneous deutero-canonical elements. The deutero-canonical elements "watered down" the force of predictive prophecy and fulfillment found in the Book of Daniel. Finally, if the Septuagint is a corrupt form of the Book of Daniel, then the Masoretic Text preserves the original text, which would preexist the Septuagint, and therefore date the Book of Daniel years before the Septuagint ever appeared.
Where did the author of the Book of Daniel get this subtle idea of using Aramaic in chiasm with Hebrew? The author may have derived the idea from the single verse in Jeremiah that is written in Aramaic, which provides chiasm and parallel for its own immediate context.