Some on-screen text is translated; I remember things like the competition award certificates being shown. Honestly I don't remember there being much of it in the first place, or anything significant being left untranslated, and I only rewatched the series last week.Thanks.
I'm of the opinion that subtitles should be as unobtrusive as possible while still being readable (death to yellow), and those seem okay to me.
But I regard the translation of on-screen text as a kind of bare minimum to be expected from a professional commercial anime release. Having said that, if these discs have been authored by software that can only display one line of subtitles at a time, on-screen translations appearing while dialogue is being subtitled would cause the dialogue subtitle to "blink" off and on again. Had that joy on my Anthem of the Heart disc. Thankfully, these issues don't seem to have affected any recent discs.
I might get it anyway as it's cheap and I like Kyoto Animation.