Flashcard science is actually a surprisingly broad and well-researched topic! There are lots of modifications that could be added to a program like this to help you learn faster, but weren't a good fit for this tutorial.
The example programs given here should be a good start, but if you'd looking for inspiration on creating your own flashcards, or making modifications to this example program, you can check out the following links.
- Pyshuffle: an extension of the program in shown this guide, which shuffles the vocabulary within card templates to create many similar versions of each card.
- Flashcards (Wikipedia): discusses different kinds of cards and various spaced repetition systems, such as the Leitner system.
- The Right Time to Learn (NIH): if you'd like to get really technical, this is a survey paper on the science of spaced repetition learning
- Anki: well known open-source spaced repetition software
This guide uses the Yasashisa Gothic (やさしさゴシック) font. It's free for both personal and commercial projects, and uses the IPA license.
IPA summary from TLDRLegal:
The IPA license applies only to font programs and allows for a great deal of freedom in distributing them, both commercially and non-commercially. You cannot change the name of redistributed versions of the original software and must include a copy of the license, however.