Crossword Genius

Language usable for a letter to an aunt (5)

Ross

I believe the answer is:

bantu

I'm a little stuck... Click here to teach me more about this clue!

'language' is the definition.
(Bantu is an example)

'letter to an aunt' is the wordplay.
'letter' becomes 'b'.
'aunt' becomes 'tu' (I can't justify this - if you can you should believe this answer much more).
'b'+'an'+'tu'='BANTU'

'usable for a' is the link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.

Can you help me to learn more?

(Other definitions for bantu that I've seen before include "Native African language" , "A language and people of Africa" , "10 across language" , "Group of Niger-Congo languages" , "African language group" .)

I've seen this clue in the Evening Standard.
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