This question is so unclear that I'm not sure you know what you're doing.
I doubt any DS game uses deliberately encrypted text. Many games will probably use their own encoding instead of standard Shift-JIS or ASCII or Unicode. And many games will also use compression, which isn't really the same thing as encryption – but if you don't know the specifics of the compression algorithm, then it might as well be.
As for Dragon Quest V, I'm sure someone has tried to translate it by now and has released some sort of tools.
In any case if you are serious about doing translation, especially if it's stuff that no one's translated before, you probably shouldn't be using Android