I finally watched my copy of the film today. As a result, I've struck through the entirety of a post that I wrote here in reaction to the above quote. Truly, I profusely apologise to Anime Limited for my premature reaction.On-Gaku: Our Sound has bits of unsubbed dialogue, which is pretty noticeable in one scene. There's are two instances of songs which aren't subtitled
Further to the quote above, I can now see that the unsubbed dialogue is simply the same phrase being repeated over and over in one scene; it's subtitled initially so that viewers can understand it, but then stops because they've probably gotten the idea by that point.
As for the two unsubbed song performances, the first is a partial repeat of a song that has already been subtitled in full earlier in the film, and the second unsubbed performance has vocals that are just improvised gibberish and are not even words, thus making it impossible to translate.
In closing, Anime Limited's Blu-ray release hugely improves the overall quality of the translation in comparison with the Scotland Loves Anime Online stream that was offered during last year's festival, which was sometimes very rough and unpolished. In my view, the company has done a brilliant film proud, and I apologise wholeheartedly for my initial kneejerk response.