Language specific pictures

I have some localized bitmaps (bitmaps containig text with is different in different languages).

In example that code:

!define MUI_WELCOMEFINISHPAGE_BITMAP "media\img\3a.bmp";

How to change it to use localized version of bitmap?

I tried something like that:

!define MUI_WELCOMEFINISHPAGE_BITMAP "$(BmpLeftBanner)";

LangString BmpLeftBanner ${LANG_POLISH} "media\img\3a_pl.bmp"

LangString BmpLeftBanner ${LANG_ENGLISH} "media\img\3a_en.bmp"

But it do not work.
I want bitmap from different file depending on selected language version.

you can probably use MUI_PAGE_CUSTOMFUNCTION_PRE and overwrite MUI's default bitmap (bitmaps for all langs need to be included so you can only check at runtime)