Version:           1.10.1 (using 4.1.1 (KDE 4.1.1) "release 31.2", KDE:KDE4:Factory:Desktop / openSUSE_Factory)
Compiler:          gcc
OS:                Linux (i686) release 2.6.25.11-0.1-pae

Kmail uses English spell checker by default. But a lot of people have a different mother tongue. Please, set the default spell checking engine (if available) to the locale.
You can find out this by typing: `echo $LC_ALL`.

And interesting that in my profile the default was English, but when I hit the "reply" button, the engine used the correct, Hungarian dictionary.
I don't know why, but it didn't work for the "new message" and the "forward" functions, these used the default dictionary.