>> "at all" is only used in negative sentence or question << That's not true. But mostly yes. Although, the first "negotiators" sentence implies a negative meaning, meaning they probably won't make it. The second "Spanish" s has a more implied and slight negative meaning, because "a little" usually makes people who expect a postive answer disappointed. The two above are not positive "positive-sentence" examples but actually somewhat negative-"at all" as an adverb means substantially, radically, at the very beginning, fundametally, first off, etc. The Chinese educators are right at all. The Chinese educators get it wrong at all. It could also equal of "anything", "any possibility", if you get any information from Professor B at all, you let me know.

Easiest to explain this is with the direct Chinese translation: at all = 完全(都不) ； 一点(都不)。。。; 一点点（可能性，能力，机会等等）（都没有） I don't understand this at all. 我完全都不懂。 You are fortunate to be able to speak even a little Spanish （at all). 在这里 "at all" 是多余的。这个句子可以写成： You are fortunate to be able to speak even a little Spanish。 你幸运你能够讲一点点西班牙文。 You are fortunate to be able to speak even a little Spanish at all. 在这个句子，“at all" 是用来强掉你一点点西班牙文都不会讲是不稀奇的。你会讲一点点算是非常好的的意思。 我的解释不清楚请你再问。

at all means in any way; to any degree or extent: I cannot come at all. He does not eat eggs at all.