Well, first, this "code" or "formula" is specific to Germany and not official. If it were, it would be illegal. So any number you pulled is a rough estimation of a specific person or book. If your employer did not hire the very same person or read the very same book, it's a guesstimate at best.
The next employer might not use the same deciphering tool you use and might come to a different number.
In addition, leaving out a quality might mean you sucked, or it might mean the company did not see that quality as important. If it is important to your next job, you might want it to be put in, even if it's just an average remark.
The Arbeitszeugnis is something your employer creates. You have the right to one, you are entitled to anything in there not being a hindrance to further employment (hence the codified ratings that all sound positive at face value). If you are not happy with what is in it, your first step would be to contact your employer and suggest specific improvements. If it's minor corrections, you have a good chance of them saying yes, because writing an Arbeitszeugnis is a pain and if HR can make you happy by changing minor details... why not, it's not as if they will make decisions based on it.
If you are not happy with it and HR is not willing to incorporate your constructive change request, you will need a lawyer specialized in employment law. A nice letterhead might bring HR's attention to the fact that it's not worth it to argue with you over minor details, if not, you might go to court over it. That's not exactly rare.
Translating a German Arbeitszeugnis to English is complex. As in German, taking it at face value is pretty much a lie. If the English counterpart does not know the code, it's useless, translating it will corrupt the code. I mean just put a few sentences into Google Translate then go back and forth and see what I mean. Translating texts that include hidden messages will be bad for the message. So there is nothing illegal in translating a text correctly into English. I just don't think it's possible with a German Arbeitszeugnis. The words will translate, the meaning will be gone. I would definitely attach it as it also confirms employment dates, though.