Tunning dict files will take these actions:

1. If a dictationary have a dict.dz file, uncompress it and split it

2. If a  dictationary have a dict or index file great then 1m then split it

 

After tuning jStarDict will access these files much faster them before. 

 

If you don't want to do this in your phone, you can:

1.Do it in your desktop by importing the dict to your desktop version of jStarDict then export it to your phone

or 

2. Turn of the tuning in Setting form.