The sentence "Your English must be good." has two meanings. 1. Requirement. In this case, you could replace the word "must" with "has to" or "needs to". A native speaker would be more likely to choose one of those phrases than the word "must", to avoid confusion with the second meaning: 2. Supposition. This is a more likely meaning of the sentence. It's the same as "I suppose your English is good" or "I bet your English is good." This is something you say to someone because you have a reason to believe their English is already good (for example, they lived in America for a year).

You are mixing up translation of müssen and haben. Your English must be good has a sense of if you are able to say that well your English must be good. Or you must have good English to qualify for this position or job. An advert would never state your English has to good. It would state good standard of English essential. I hope this helps. Louise Native English speaker

You can say either “your English must be good” or “your English has to be good”. You don’t use an infinitive in this statement, have is incorrect

If you're saying that it's a requirement for you to have good English, it would be 'your English has to be good' or 'you must have/speak good English'. Eg: to read Charles Dickens in the original, your English has to be good. You can say 'your English must be good' too but this can also have a slightly different meaning. It can mean that you're making a guess/assumption about a person's English. Eg: 'You read Dickens in the original? Wow, your English must be good!' In this case you don't KNOW that they have good English, but you're guessing that they do because they're able to read Dickens.

I think “your English has to be good” would be correct