I gave up saying "good job" many years ago. Some of my clients and their families may have noticed I don't use praise in my therapy sessions! The reason: copious research showing that praise and reward systems can actually undermine intrinsic motivation (that's wanting to do something for the sake of it). I want to make it intrinsically motivating to communicate; I want to keep learning fun. And I've learned that praise can actually backfire.
So what do I do instead? I give meaningful, genuine feedback that doesn't have any value judgement in it. I try to keep it framed as a comment about what I observed. I might say "you did it!" or "wow, you tried that!" or "I heard the snake sound!" or "oops, that time your mouth got a little mixed up!". Of course I do this with genuine enthusiasm, smiles, and a sense of humour. I might also ask the child "did you feel that?" to encourage self-reflection and self-assessment. Because I want kids to be able to decide if they think they did a good job, not just try to please me.
If you're interested in learning more about this research, I strongly recommend the book "Punished by Rewards" by Alfie Kohn which details this topic as it applies to schools, parenting, and workplaces.