There's always a relevant xkcd.

If it's actively glowing blue, I don't think it's safe to handle.

Somebody casted Repair on the rod

What if it was stored in a fridge

Hmm, I think as a DM I would roll an arcana check to see if the wizard would conceivably have heard of radiation from arcane studies. It's reasonable to assume people with arcane knowledge would be the first to hear about the strange metal chunks that everyone keeps dying around. One of them would have had to have come up with a word, if not some variation on "death cursed"

I'd personally translate it to the closest word they have.

If I decided they didn't have a word that was directly equivalent, in this case I'd use the closest word, "light-emitting".

That is a really good question...

I feel like radiation should have some sort of translatable element as a generic radiant danger, but for the rest... if it doesn't make sense without context in the source language, does it make sense after 'comprehend language'? Kinda feels like we need a 'comprehend science' or something if they wanted to grasp the idea of specific elements and units of measure.

Haha good one. "Punny answer."

"Something something - anything if you're brave enough"

If the rod is glowing, probably a fuckton.

It's technically slightly visible in air; if actually visible at all in air it means the level of radiation is ludicrously deadly

I am guessing the idea is to induce terror in the holder such that, if they did not intend to hold a vial of Co 60, they would not mess with it further. It conveys the appropriate level of danger, if not an appropriate set of handling instructions.

Edit: So I looked it up and I misunderstood: if you can read that (especially by the blue glow) then its rapidly killing you. I really don't understand how dangerous some radiation is lmao.

If your are very lucky, you can find one by the side of the road in Australia.