Many dictionary programs provide a drop-down visible in the main screen that allows one to switch between two or more dictionaries. But the average user does not need more than one dictionary at the time so I thought that it will be better to keep the main screen simpler/clean.
Whenever you will need to switch between dictionaries you should tap your device menu button then to choose 'Dictionary' option. It will show you a list of the installed dictionaries where you can select whatever dictionary you might like.
If you are curious to know many info about one dictionary (e.g. when it was created, the use terms and the license, its author, etc) then you should tap 'Info' button visible in the select dictionary screen as shown earlier. You will get a screen that looks like the following:
When the application is first installed it does not have any preintalled dictionary. Also one might want to install one/more additional dictionaries later.
You can install a dictionary by tapping the 'Install new' button as shows in the select dictionary screen.
You can check more than one dictionary at a time if you want a parallel installation.
Throughout the whole installation process you will be informed of the installation status by a progress dialog. There you can find how many files are simoultaneous downloading, the average download speed, the procent done and the estimated time to finish.