Engrish!

No, Pidgin English.

Kayako said:
It's not poorly translated. Shampoo is Chinese, she doesn't speak proper Japanese, so her speech should be written like this when translated.

Shampoo's lines are ok, like you said, but Ranma's lines are in pidgin english. Not poorly translated, per say, but frowned upon by some as its not customary with the Translation/Edition guidelines for professional works.