CHARACTER SET "WE8ISO8859P1" is used for SQL text, and the data types such as CHAR, nad VARCHAR2

The National character set is used for the data types NCHAR, and NVARCHAR2. In general, as with regular character set, it cannot be changed.

As I said, both usages depend upon the application requirements.
Assume your database stores both ENGLISH and FRENCH characters. Then probably you need to go for UTF16 or UTF8.

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