Choosing character set for database

Is there any clear performance difference of using multi-byte
character set (such as UTF-8) and single-byte (e.g. SQL_ASCII,
LATIN2). Why there is no UTF-32 (generally more space for chars, but
faster to calculate than multibyte ?) ? I found only at Oracle 11g
documentation that:

"For best performance, choose a character set that avoids character
set conversion and uses the most efficient encoding for the languages
desired. Single-byte character sets result in better performance than
multibyte character sets, and they also are the most efficient in
terms of space requirements. However, single-byte character sets limit
how many languages you can support."

Regards,
Grzegorz Sz.