Thế file txt là Unicode chứ?
BTW:
DSReader is pretty simple, so perhaps you're overthinking it a bit. Here's a quick guide to getting it working:
1. Create a folder on the root of your card called "DSReader"
2. Copy (NOT move) fonts from "C:\Windows\fonts" to the DSReader folder. I mostly use Arial, but you're free to use whichever font you wish.
3. Copy and paste your *.txt files directly to your card. They can go anywhere on your card, not just the DSReader folder.
That should be all there is to it. Launch DSReader.nds, press A (or drag up on the touchscreen) to open the menu, and load your *.txt file from there.
The only other thing to keep in mind is that bookmarks only work if the filename of the *.txt file has no spaces in it.
If you get strange characters when reading (for quote marks or other symbols), then open the *.txt file in Wordpad, do a File - Save As, and for the "Save As Type" option box use "text document - MS-DOS format"
I'm assuming your ebooks are in *.txt format already. If not, we'll need to know what format they're currently in so we can convert correctly.