"The bird is not dangerous but it is vicious."
Translation:Qobbe' bo'Degh 'ach naS.
Yes. 'ach is one of those words that has an alternative. 'a is used in exactly the same ways and officially carries the same meaning and implications. Though, to me personally, it always feels more casual, and I certainly alternate them based on how casual I want something to feel. Dr. Okrand has not stated that this is accurate and I won't claim that all skilled Klignonists share this sentiment (though I'll bet at least a few do).
"Qobbe' 'ach naS bo'Degh" was not accepted, and I'm not sure why. I suppose it's because the second half of the compound sentence was meant to have "it" as its subject, and I was trying to make bo'Degh the subject of both halves of the compound sentence instead. Would that work, or does a 'compound subject' (so to speak) not work with 'ach because it's meant to join only complete sentences?
'ach and 'ej join complete sentences.
So Qobbe' 'ach naS bo'Degh is more like "It's dangerous, and the bird is vicious."
Sometimes you'll find two sentences joined by 'ach or 'ej where the subject is only mentioned in the second sentence, but I think it's clearer to mention it in the first one.
qatlho'! I think my mind keeps trying to fit everything into OVS word order, and thus, I try to put the subject last (my somewhat limited experience with Japanese may be influencing this). I just have to remember that (1) it's always better to mention the subject up front for clarity's sake, and also that (2) "it" and "he" require neither overtly stated pronouns nor verb conjugations/prefixes in Klingon, meaning that a lone stative verb, while it can look like a fragment, can actually also be a full sentence in itself.