What's weird is that I've noticed that a lot of my JP imports are locked out of US systems but not PAL ones.
JP Gunstar Heroes has both the Japanese and English versions on the cartridge, but it won't boot on a system set to USA mode (English/60hz). If I start the console in English/50hz, though, I can get it to load the English script since it thinks it's running on a PAL system, and then I can flip it to English/60hz after it boots to play at the correct speed. And if I just start it in Japanese/60hz, it loads the Japanese script.
You can change the script for some games on the fly if you have a switch installed. Flipping between Japanese and English on the Streets of Rage 1 intro will change the text as it's still loading and scrolling, mixing both languages as you flip them.