"Tien olifanten, dat is te veel."
Translation:Ten elephants, that is too many.
You're right! (Sie haben recht!) These sentences would be better served to have colons rather than commas, or just write them as a sentence fragment and a sentence; or better yet, leave out 'that' entirely, along with any internal punctuation.
Nine elephants: that is not enough. Ten elephants: that is too many. Nine elephants. That is not enough. Ten elephants. That is too many. Nine elephants is not enough. Ten elephants is too many.
I agree with the person above. Nine and a half or nine and three quarters seems to be an adequate number of elephants.