Do not look into NVARCHAR2! Oracle does not recommend using this data type, especially not in a database that is already Unicode (AL32UTF8).
You can, of course, create indexes on Hebrew data. But note that standard indexes will be sorted according to binary order of Hebrew letters in Unicode. This order is not necessarily the correct linguistic order, especially when accents are involved.
Varchar2; is something difficult for me. Reason why is I need to make change in my application throughout to accept this design change.
My need of Index on Hebrew Data:
Basically I am going to implement a Full-Text Search environment. For full-text searching; I am having a plugin which implements Lucene Algorithm of Indexing.
The Index writing will not be useful until the table is indexed and well-functional.
"But note that standard indexes will be sorted according to binary order of Hebrew letters in Unicode."
So does it means we are not going to index on actual data (Data in Hebrew)??
Why do you want to implement full-text search when it is already provided by the Oracle Text feature built into the database?
By indexing Hebrew data, do you mean a standard binary index or an Oracle Text domain index? These are quite different indexes with different purposes.