Daniel 2.4 is a pivotal verse:
“The Chaldeans answered the king in Aramaic: O king, live forever! Tell the dream to your servants and we will give the interpretation” (Daniel 2.4).
The first part of the verse still belongs to the Hebrew section.
The change of language occurs precisely with the Chaldeans’ reply.
From the words introducing their speech in Aramaic, the book continues in that language to the end of Daniel 7.
The general distribution is therefore:
Daniel 1.1-2.4a: Hebrew;
Daniel 2.4b-7.28: Aramaic;
Daniel 8.1-12.13: Hebrew.
This is therefore not a matter of a few foreign expressions inserted here and there in a Hebrew text, but of a continuous Aramaic section covering nearly six chapters.