[neurostar]

Now WinterBoard support skinning international keyboard artwork.
You can put modified pngs to something like /Domains/Textinput_ko/.
You can get list of file name for pngs with odcctools (thanks to Saurk).

Install odcctools through Cydia.
On ssh or terminal, strings TextInput_ko (executable file for each language).

For Korean keyboard, I got followings.

kb-std-abc-intl-ko.png
kb-std-abc-ko.png
kb-std-ko-active-fg-1.png
kb-std-ko-shift-active-fg-1.png
kb-std-ko-shift.png
kb-std-ko.png
kb-std-landscape-abc-intl-ko.png
kb-std-landscape-abc-ko.png
kb-std-landscape-ko.png
kb-std-landscape-number-pad-abc-ko.png
kb-std-landscape-won-ko.png
kb-std-number-pad-abc-ko.png
kb-std-shift-landscape-ko.png
kb-std-trans-ko-shift.png
kb-std-trans-ko.png
kb-std-trans-landscape-ko.png
kb-std-trans-shift-landscape-ko.png
kb-std-won-ko.png
kb-trans-abc-intl.png
kb-trans-abc-ko.png
numbers.png
symbols.png
trans-abc-intl-landscape-ko.png
trans-abc-landscape-ko.png

tested and works well.

For Russian,

kb-std-abc-intl-ru.png
kb-std-abc-ru.png
kb-std-landscape-abc-intl-ru.png
kb-std-landscape-abc-ru.png
kb-std-landscape-number-pad-abc-ru.png
kb-std-landscape-ru-active-bg-pop-center.png
kb-std-landscape-ru-active-bg-pop-left.png
kb-std-landscape-ru-active-bg-pop-right.png
kb-std-landscape-ru.png
kb-std-landscape-trans-ru.png
kb-std-number-pad-abc-ru.png
kb-std-ru-active-bg-main.png
kb-std-ru-active-bg-pop-center-wide.png
kb-std-ru-active-bg-pop-center.png
kb-std-ru-active-bg-pop-left.png
kb-std-ru-active-bg-pop-right.png
kb-std-ru-active-fg-1.png
kb-std-ru-shift-locked.png
kb-std-ru-shift.png
kb-std-ru-trans.png
kb-std-ru.png
sm-shift-press.png
sm-shift.png
trans-abc-intl-landscape-ru.png
trans-abc-intl-ru.png
trans-abc-landscape-ru.png
trans-abc-ru.png
trans-delete-active-ru.png
trans-delete.png
trans-shift-active.png
trans-shift-ru.png