Here's a trait to use as reference (the xml resource is heavily commented... it's actually an UNKN resource though).

It has no gameplay value, it's just an example (and "requires" my Napping Mat mod, otherwise you'll get a warning,
actually it will make the mat unusable by Sims who don't have the trait, so it's just bad)

DON'T SCREW YOUR SAVEGAMES ! Read the description of the mod.

EDIT: I've added empty thumbnail icons to use as bases. (Re-uploaded with light blue background for the big icon)
Re-uploaded the example trait (I had forgot to include the STBL resources for most languages)

EDIT: Uploaded a "skeleton" package to use as starting point. It should shorten a bit the steps needed.
Remember to rename (and re-hash using the new names) all resources using unique names.

You are a real genius!!! Now sims have personality!
Would you like to create some custom moodlets like unrequited love, jealous , missing someone etc or even a custom moodlet manager like this? In Sim3 sims always have the equal relationship which is often isn't in real life. Adding these moodlets may be helpful.
I do not know any programming at all... anyway, I will try my best to study your tutorial. Thank you for all your masterpieces!

Great mod!

So, about how to create custom trait.

Is that all I got to do to make working trait?

How do I make custom trait so that it shows up in the "regular Create a Household trait" just like your Japanese Culture Traits?

Cause I see it shows up without this mod.

I just want to create custom trait by myself.

Amazing!
I'm not going to touch this - it scars me! But, AMAZING!

This is so great, I can't wait to use it! *eagerly awaits next parts of the tutorial*

You've been busy! <3

Thanks for creating this! Good job!

Thank you so much! It's great that Sims 3 is still getting support, you're one of the best when it comes to making new stuff for this game. I am honestly surprised that it took so long to make custom traits for the game. I mean, we had the one Hypochondria trait, but that was it.

Anyway, thanks for all your work, and thanks for keeping the Sims 3 alive with your additions!

Thank you for making this, but it's to complex for me LOL It is a miracle that i manage to walk and chew gum at the same time 8D Keep making mods ;)

Thank you for the time and effort of making this tutorial! Off to try to make a "drow-trait"

Thanks

So i managed to make an alcoholic trait. It shows up in game but it doesn`t actually _do_ anything. Could anyone give me a hint of how to make it "push" the sim to drink if having this trait?

I think I'll use your great work to support the Traits part of a mod I'm making. Genius !

Tyvm for working on this! :)

When I look in your code with Reflector, I see that it's supposed to add traits to an enum, which I guess is TraitNames, but when I use it in-game, the traits are indeed loaded and I can select the not-hidden ones when editing a sim's traits, but they still aren't in the TraitNames Enum.
Therefore, the other methods in the game can't acknowledge its existence. For example :
returns true, but
returns false.
Do you have a way to use the trait in new methods ? For example, to tset if a specified sim has it or not ?

Just in case someone is wondering after seeing Armise's comment, you can cast your trait GUID as a TraitNames type and functions will still work with it. The following works: