The OCR assets should have been copied the very first time the OCR feature was invoked. One thing to try is to simply uninstall and re-install the app. Maybe it was just a one-time glitch.

If that doesn't work, check to see if the following files exist:

Where <sdcard> will be something like /sdcard or /sdcard1 depending on your device.

If one or more of those files do not exist for some reason you may download the source code project and copy the files from the ocr_manga_reader\assets folder.