Aniplex themselves are too lazy to subtitle them. Only the very first Monogatari has the commentaries subtitled. Nisemono doesn't even include them, but I believe they added them back in (unsubbed) in subsequent sets.
It's why I boycotted every release, even though I would be a prime candidate to buy the series.
Also, it's like the white whale of anime subbing. At least several people have tried to sub the commentaries and everyone has failed. lol
I joke, but I'm at a point where I would be willing to do a bounty on them... but at this point, I don't even know what the anime subbing community is like anymore. They all work for CR or Funimation I assume.
I'd be willing to try my hand at TLing that, but I guess doing it without JP subs would be a pain because of how much the show likes its puns at times.