KMail dictionary selection doesn't apply to subject

Hello list,

I have British English selected in my Identities, and KMail does use that 
choice in the body of a composer window, but the subject line is checked 
against US English. Whether the subject should be checked at all is debatable, 
but if it is it should use the same dictionary as the body.

It's not a serious problem, but I thought I'd mention it in case a developer 
is watching.

-- 
Gentoo testing
sys-kernel/gentoo-sources 4.18.10
QT 5.11, KDE frameworks 5.50.0, KDE plasma 5.13.5
KMail 5.9.1 (gentoo 18.08.1), akonadi 18.08.1
x11-drivers/xf86-video-amdgpu 18.1.0, dev-libs/amdgpu-pro-opencl 18.20.606296