Start talking back in a foreign language (5)

I believe the answer is:

latin

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'a foreign language' is the definition.
(I've seen this before)

'start talking back in' is the wordplay.
'start talking' becomes 'tal' (I can't explain this - if you can you should believe this answer much more).
'back' is a reversal indicator.
'tal' written backwards gives 'lat'.
'lat'+'in'='LATIN'

Can you help me to learn more?

(Other definitions for latin that I've seen before include "Romantic language" , "Cicero's tongue" , "Language of Cicero" , "language class" , "Virgil's tongue" .)

I've seen this clue in The Globe and Mail.

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