I found this next passage about writing dialogue from a screenwriting book for live action movies and television.
NOT EVERYONE CAN WRITE GOOD DIALOGUEI have found this equally true in animation. Hardly anyone is good at writing natural and entertaining dialogue, let alone writing it in character. Most animation writers resort to catch phrases and off the cuff pop culture references that could be said by any character.
Some things you just have to have a talent for - like writing dialogue, or writing melodies. There are all kinds of good musicians, but very few among them can invent catchy melodies. The ones that did are immortal. Character design in cartoons is like this. You just have to have a knack for it. I don't think it can be taught.
WRITING PRODUCES STILTED DIALOGUE BY ITS VERY ACT
I've mentioned before that I have found this to be the case for myself. When I try to write dialogue at the keyboard, it comes out stiff and stilted. Once I know the context and meaning of a scene, I do much better by walking around the room and improvising the dialogue while acting the scene out more spontaneously. Speech must use a different part of the brain than writing.
YOU CAN'T BE TAUGHT, BUT YOU CAN IMPROVE YOUR NATURAL ABILITY BY KEEN OBSERVATION
I think to be naturally good at something like dialogue, you have to have not only the natural gift, but a keen interest and fascination with how people speak. You have to be constantly aware of how different people express themselves and be able to pick out who is entertaining, how and why they are and then how to edit out the boring parts.
By Wolf Rilla