Such language in writer's essay! (4)

I believe the answer is:

erse

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'such language' is the definition.
'erse' can be an answer for 'language' (historical term for Scottish Gaelic). I am unsure of the 'such' bit.

'in writer's essay' is the wordplay.
'in' indicates the answer is hidden within the clue.
'ERSE' is hidden within 'writers essay'.

Can you help me to learn more?

(Other definitions for erse that I've seen before include "Possibly the language" , "Kind of Gaelic for seer" , "Old Scots or Irish Gaelic" , "Celtic tongue" , "Old Celtic language" .)

I've seen this clue in The Telegraph.

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