Hi! Thanks for this contribution!

Your (non-long) descriptions are too long, generally. (The long descriptions are fine).

Don’t include a period at the end. Don’t include newline characters. Capitalize the first character. For brevity, don’t repeat the name of package — just describe what it does.
— ­https://nixos.org/nixpkgs/manual/#sec-standard-meta-attributes

Andika's description would be fine after removing its name from it. Doulos' description isn't far from being short enough, Charis' is definitely too long.

You will need to add yourself to maintainers/maintainer-list.nix. (This is why the CI barked.)

Charis doesn't build here:

building '/nix/store/irh4ynr3igpj80yl789f3h5c4qpf5qrh-charis-sil-5.000.drv'...
trying https://software.sil.org/downloads/r/charis/CharisSIL-5.000.zip
[...]
fixed-output derivation produced path '/nix/store/22sblvspmkf0xhczvc20fm545gi06kxx-charis-sil-5.000'
with sha256 hash '1a220s8n0flvcdkazqf5g10v6r55s2an308slvvarynpj6l7x27n' instead of the
expected hash '1zw5n52xgii2lh325aqzlb0dj0fdybarkqj7hznnx1xxb6wmgbql'
error: build of '/nix/store/irh4ynr3igpj80yl789f3h5c4qpf5qrh-charis-sil-5.000.drv' failed

The other two are fine.

For anyone wondering why Andika isn't suffixed with -sil while the other two are, it seems that upstream names them like that. The derivation seems to be heavily inspired from Gentium's, if anyone wonders about the way this is written.

@f--t, If you have any questions, please ask. With those nitpicks taken care of I think this can be merged.

@samueldr Thank you for the feedback!
The requested changes have been made, please let me know if further revisions are required.
I used the tagline from each font's homepage as the short description.

Almost all good! It builds fine locally. Only one thing left from my original comment:

You will need to [add yourself to maintainers/maintainer-list.nix]. (This is why the CI barked.)

From the nixpkgs manual, Standard meta-attributes

maintainers
A list of names and e-mail addresses of the maintainers of this Nix expression. If you would like to be a maintainer of a package, you may want to add yourself to maintainers/maintainer-list.nix and write something like [ stdenv.lib.maintainers.alice stdenv.lib.maintainers.bob ].

As there is no entry for f--t in the maintainers list, the current maintainer attribute on your three packages does not evaluate. You're in luck, since - is valid in identifiers you can use it there!

After you add yourself, may ask of you to squash your commits?

I missed that all the fonts were added in one commit. Not a big deal, and we can live with that, but in the future it is preferred to have one commit per package.

Thanks for bringing me up to speed with the contributions guidelines. I could separate the commits if that's needed; otherwise, I think that should be it.

Ah, thanks! Merging it as such even if a bit out of the ordinary with regards to the commits structure. I'm sure next contribution they'll be just fine :).

Thanks again for the contribution!