I knew I was taking a bit of a risk with the German pop-ups, so I tried to hold back from changing anything that would be important during gameplay (like the score and lives display). I knew "Game Over" and "Stage Clear" were completely safe, and also did the boss warning message since it was more cosmetic than anything else (and there was no threat during its appearance). Maybe also changing the end of stage bonuses was pushing it, but I wrote those in the manual too.
I think you're the first person to mention reading it, actually...
Oh, I just noticed that the Jam Submission page for this game has its own download button, but doesn't show my desperate plea to read the manual first, and now I'm starting to wonder if nobody else did. I hope that hasn't affected my ratings too badly...