There are many ways in which you can contribute to theSlate.
If you find a bug in theSlate and you can reproduce it, file a report at the issue tracker and we'll have a look at it.
Go ahead and fork the repository and make some code changes. When you've added a feature or fixed a bug, make a pull request and I'll take a look at it and merge it.
If you speak another language, head to the translation portal and shoot me a message so I can give you translation permissions.