"They decided that tribbles are forbidden."
Translation:yIHmey lutuchlu' 'e' luwuq.
I may need clarification. I'm a little confused by your question. Particularly by your switch from talking about the "subject", but then saying "object". I assume it should "subject" both times? In any case, I'll list some facts and if you have questions about any of these, let us know.
-Viewing this as two sentences (which is a fine way of viewing it), the English translation of the Klingon would be "Tribbles are forbidden. They decided that."
-In the first sentence, the tribbles are not doing the forbidding, they are the things being forbidden, so they are the object of the first sentence and properly appear before the verb.
-In the second sentence, 'e' is the object and is before the verb so, in the right place.
-In the second sentence, "they" is the subject, but it is not clear who "they" are.
-The tribbles are definitely not the "they" referred to in the subject of the second sentence, but if the intent was to say that the tribbles had made the decision, then, yes, they could appear after wuq.
If that doesn't clarify things for you, then please ask again in a different way and we'll see if we can figure out how to understand each other.
When you see the passive voice in English (noun is verbed) being translated with -lu' in Klingon, don't think that Klingon has a passive voice. It doesn't. Instead, -lu' indicates an indefinite subject — the subject remains unspecified.
While you can translate the sentence yIHmey lutuchlu' with tribbles were forbidden, you can also translate it in the active voice as one forbids tribbles. This more accurately mirrors the Klingon grammar and avoids the temptation of trying to find a passive voice in Klingon.
yIHmey lutuchlu' one forbids tribbles
'e' luwuq they decide that
The subject of the second sub-sentence is they: those who decided to forbid tribbles. The first sub-sentence has no subject at all.