I'd say it's better than borderline. It's clear that some effort went into it, and the grammatical oddities give it a certain poetic quality, whether or not that was an accident. It's quite appropriate for an old song.
The Klingon in Star Trek: The Motion Picture is perfectly correct by definition, since it is the source that the language was built on. Apart from that, Okrand wrote dialogue and sometimes coached actors for TSFS, TFF, TUC and STID and a few episodes of Enterprise (The Augments, Affliction and Divergence, I believe), so those are all excellent, even if some of it had to be retconned after the fact due to mistakes or editing. Apart from that, there are a handful of epiodes that only use a handful of phrases, which are often correct.
The deleted Klingon scenes in STXI are a bit of a mixed bag, likely due to editing which was never fixed since the scenes ended up being cut. The scene where the Klingons tell Nero and the crippled Narada to surrender is excellent, the prison scene is weird.
The Final Frontier is the gleaming example of well-written and excellently performed tlhIngan Hol dialogue, so it's a real shame it isn't a better movie.
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Thank you for all that! You must be an expert in Klingon language! I am impressed.
