Function
The link the email delivers
That locale, or the default locale when none can be read
Better Auth runs the email callbacks without any request locale, but every
account form passes a locale-qualified callbackURL (/es/learning,
/es/reset-password), and Better Auth copies it into the link. The first
segment of that path is the locale the learner acted in.
An email whose link points straight at a page rather than at the auth API —
the password-changed notice, which opens /es/forgot-password — carries no
callbackURL at all. Its own path already spells the locale, so that is
read next. A /api/auth/... link falls past it, api being no locale.
The locale an account email must be written in, read from the link it carries.