Here's the code I use to run all of my birthday bots: both the Animal Crossing (in its two languages) and the Fire Emblem ones.
Please note that the images that the bot posts are done mostly manually, by doing a simple GET request to obtain who celebrates their birthday on a certain day.
Also, this code uses API keys provided by the Twitter Developers Portal to work, which are private therefore I can't share them, so this code won't work if you try to run it yourself as it is right now.
Finally, the database folder contains all files that the main program reads. They're incomplete (done intentionally, as an example) and only have a few characters, but that's more than enough to understand the whole process, though I can still upload the full databases if you ask for them!
I uploaded this code to GitHub in case anyone's curious about how my bots work and, with just a bit of knowledge in programming, you'll see that it's actually pretty easy and takes fewer lines of code than you'd expect!
I've tried to leave enough comments so anyone can understand what the bot does and how it works. Still, feel free to ask me any questions!