For long adjectives, both in comparative and superlative forms, we can convey the opposites of MORE THAN and THE MOST with LESS THAN and THE LEAST, respectively. Now, what about the short adjectives? How are we supposed to convey the same for the comparative and superlative forms?

Suppose I give you these examples:

John is happier than Paul.

Sarah is the tallest student in the school.
John is less happy than Paul. / John is not as happy as Paul.

Sarah is the shortest student in the school.

(You could theoretically say "the least tall student", but it would be unnatural. With short and simple adjectives there's very likely to be another adjective that means the opposite. For example: "thinnest" rather than "least fat", "dumbest" rather than "least smart", etc.)
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Thanks, Mr. Wordy. So, it's grammatically correct, isn't it?

You're right, though -- it indeed sounds unnatural.
Yep, it's grammatically correct. I suppose "least tall" might be feasible in some situation where "shortest" (or "lowest", or "smallest", or similar) doesn't work for some reason. It doesn't sound quite so odd when applied to mountains, for example. I'm struggling to think of a really good example though...

Basketball players. That's probably a case where you would say least tall rather than shortest.

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