Yes.
Your diary is not testimony.
Your blood is not testimony.
Your handwriting is not testimony.
Testimony is testimony.
As mentioned elsewhere, you miss the point of the fifth amendment. It was not because self-testimony was sacred. It is because people were being tortured to get it.
Given that a diary is already written, no current harm will come to you from its use.
Now, if your question is whether this should be protected that's a question about society and whether we need to pass a new amendment. But it's not what the fifth was there for.
As mentioned elsewhere, you miss the point of the fifth amendment. It was not because self-testimony was sacred. It is because people were being tortured to get it.
Given that a diary is already written, no current harm will come to you from its use.
Now, if your question is whether this should be protected that's a question about society and whether we need to pass a new amendment. But it's not what the fifth was there for.