7ª7ég}ÇÞFf0 makes sense to me.
You are using the character set: ISO-8859-1, and thus the bytes will be decoded to the characters they are mapped to in that character set.
Your byte array is created using base 10, and java bytes are signed. This means your byte array has the following hexadecimal values (in order):
37, AA, 9A, 37, E9, 1A, AD, 67, 7D, C7, 92, DE, 46, 66, 30, 99
According to the ISO-8859-1 character set, these values map to the following:
7, ª, (nil), 7, é, (nil), SHY, g, }, Ç, (nil), Þ, F, f, 0, (nil)
Which is pretty close to what your string is actually. The
(nil) characters are not rendered in your string because the character set does not have glyphs for the corresponding values. And for the character SHY, I will assume again there is no glyph (while the standard indicates there actually should be).
Your output seems correct to me! :)
Remember, your encryption key is just a sequence of bytes. You shouldn't expect the data to be human-readable.