At the beginning the class Leetspeak is declared as an independent class instead of being an inheritor of Encoder. Just "extends" is needed.

Could you post your code using proper markdown and marking your post as having spoiler content? I passed the kata without problem.

It's not in my code. I ran the sample tests and everything is OK, but with the attempt button I got the error:
./src/test/java/EncodeTest.java:10: error: incompatible types: Leetspeak cannot be converted to Encoder
myEncoder = new Leetspeak();

Where is that line? If it is in your code, then it's wrong, check the first point you have to do:

The code must contain a Leetspeak class inherited from an Encoder abstract class.

Leetspeak cannot be converted to Encoder
myEncoder = new Leetspeak();
^
Why I´m getting this?