Varchar and multi-byte

Hi,

I have a question regarding the varchar type and the multi-byte settings.
Varchar is defined as having a maximum and variable amount of characters.
When running a multi-byte database (for example Japanese), does this
definition also apply for Japanese characters ? In other words : do you
define half the amount of bytes used ?
If so, is there an alternative with which you can define a maximum number of
bytes to be stored as opposed to characters (like in Oracle : varchar2 and
SQL Server : nvarchar) ?

Please help if you can,
Fred