I don't know if it's that bad... In my experience the English lyrics from these euro power metal bands are ~98% good, but then there's the odd line that has you reach for a thesaurus to see if that's real English or they've pulled it out of their butts, and most of the time it's the latter. It's pretty off-putting, it would be perfectly OK if that was it, but it often brings your attention to the fact that the lyrics are very weak in general.

Did some dialog work for a German game company when I was younger.

In one of the raw scripts I received from the German side, I remember staring at "medicament" for a long time, before looking it up.

So yes, I know the feeling. :)

FWIW, Kreator, Scorpions, Destruction, Sodom, and basically every other German metal band probably have better English than most native speaker groups for the past 40+ years. Americans in particular seem to do quite poorly at speaking other languages partly because to be American, particularly in cities, one needs to know several dialects given the many different creoles and vernacular groups due to the country being so massive and diverse.