Daniel 4 was in aramaic, because it is the personal testimony of Nebuchadnezzar, not the writings of Daniel.
A few aramaic words in other books because they have no parallel in Hebrew.
And yet the Bible records its pre-Babel conversations in Hebrew — there's nothing to indicate that Hebrew was spoken pre-Babel.
(IOW, that testimony could easily have been included as a Hebrew translation, if it were imperative to keep the scriptures Hebrew.)
A few aramaic words in other books because they have no parallel in Hebrew.
*nod* — Such it is with multiple-languages, if your language doesn't have a concept you borrow it from another.
I'm just really leery of the language matters most
/holy tongue
types (especially the name guys) as it comes off to me as magic-wordism
where concepts and understanding are discarded in favor of particular throat-and-mouth noises — Pentecost is an interesting counter-example to that mode of thought, IMO, as the foreigners heard the message in their own tongue, not that they were suddenly made able to understand Hebrew.