Emojis

Folders setup

Create a folder contents/myemojis/textures/font/emoji/

Image

Inside this folder you have to put your emojis, you should make them 72x72 to make sure they're not too big and they're not pixelated. But you can decide the size you want (only important thing is that height and width is not over 256.

In this example I put an image named contents/myemojis/textures/font/emoji/smile.png.

Configuration

Create a configuration file, for example contents/myemojis/myconfig.yml (you can name it whatever you want)

contents/myemojis/myconfig.yml

info:
  namespace: "myemojis"

Then add your emoji (in this example I made a smile emoji) to the list of font_images, so your file would look like this:

contents/myemojis/myconfig.yml

info:
  namespace: "myemojis"
font_images:
  smile:
    permission: 0
    show_in_gui: true
    path: "font/emoji/smile.png"
    scale_ratio: 9
    y_position: 8

scale_ratio is the final height in pixels of the emoji because 72x72 pixels is too big, You'd have to scale it but you can set 9 so Minecraft will handle it automatically. y_position is the y position in pixels, 8 should be good if you keep emoji 72x72 and scale_ratio to 9. If you have different size you'll have to tweak the y_position based on your tests.