I suppose characterset conversion doesn't occur.I suppose it does occur, otherwhise the strings would use the same amount of bytes. Note that in AL32UTF8, some (special) characters use more than one byte, so you might need more space to store the same value. Of course, you gain the advantage to be able to store (nearly) any special character of (nearly) any charset.
That way, you'll always be able to store 30 characters with respect to the needs of your charset.
DESCRIPTION NOT NULL CHAR(30 CHAR)