... acute in writing, maybe. Alternatively, there’s one’s expression when talking ... (6)

I believe the answer is:

accent

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'acute' is the definition.
(I've seen this before)

I don't understand the rest of the clue.

(Other definitions for accent that I've seen before include "Local way of pronouncing words" , "Stress, emphasis" , "Local way of speaking or enunciation" , "A localised way of speaking" , "Regional speech characteristic" .)

I've seen this clue in The Telegraph.

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