I also had problems using the Package Installer to install the translator data files to my SD card. Didn't do any real investigations as to why, but possibly because the pathnames within data.tar start with "./opt" ?
Anyway, for the translator, you need to download the following files :
translator_1.0.0-1_arm.ipk
translator_ej-data-data_1.0.0-1_arm.ipk
translator_je-data-data_1.0.0-1_arm.ipk
I guess you'll be quite happy to install the translator program to Flash, in which case it will install fine using the Package Installer. Unless the data files have been fixed, you'll need to download them to the SD using wget before installing them.
Use the procedure mentioned by Stubear above to unpack the files. You should end up with 3 directories (I think) , eljisho and ejtable (for English->Japanese) and je (Ja->En). Move these directories to /mnt/card/QtPalmtop/translator. Then give the translator a try ...
Having said that, I've found that whilst the English to Japanese translation is working fine, when I try a Japanese to English conversion, the program just bombs. So maybe these instructions are incomplete.
I'm reliably informed that the English to Japanese translations aren't too hot anyway, so I may go look for a better translation program.
Ian