As Konami is an international company with world-wide sales with it's roots in Japan, Konami needed to produce two versions of their programs, one for the Japanese market and an English version for the rest of the world.
For some games Konami decided not to produce two different language versions of a rom game, no the put both language versions in one rom cartridge.
This was a possibility because the MSX computer BIOS rom contains a land code. Using that code as identifier the game showed the English or Japanese version.
This can easily checked when using an MSX emulator. Run that emulator with Japanese or English system roms and the Japanese or English version of the game will automatically run.
Vampire Killer is one of those bilingual roms.