[RFC] send-email: UTF-8 encoding in subject line

Hi,

While using git send-email I ran into some confusion around the prompt that appears when any 8-bit (non-ASCII) content is detected.

When prompted with,

  Which 8bit encoding should I declare [UTF-8]? y
  Are you sure you want to use <y> [y/N]? y

I initially assumed this was a yes/no style confirmation and answered "y", and ignored the 'which' part (this was due to my oversight). This resulted in the charset being set to "y", which later produced a subject line like,

  =?y?q?...?=

Mail clients like Gmail still displayed the message correctly, but the mailing list archive showed the raw encoded form[1].

Afterwards, I realized the prompt expects a charset name (e.g., "UTF-8") rather than a yes/no answer, and pressing enter would have selected the default (which is UTF-8).

I had also encountered this earlier when the non-ASCII character was in the message body rather than the subject, in that case the result appeared to work fine even with the mistaken input, which made the issue less obvious to me at first.

This made me wonder whether the current UX around the prompts or input validation could be improved in any way to reduce the chance of accidental input being interpreted as a charset name.

Best, Shreyansh

[1]- https://lore.kernel.org/git/20260219181154.66814-1-shreyanshpaliwalcmsmn@gmail.com/