The spawner corpses are missing localization string. This won't affect biomass salvaging from their remains, so it's not that urgent of an issue, just looks distracting in their tooltip. Maybe some other corpses that are valid target for biomass salvaging are having this problem too.

https://cdn.imgchest.com/files/4apc5x3w994.png

This is a bug. Not in localization, but in the fact that the corpses of the biters should not be looted, but they are.
Will be fixed in the next release

Oh, and here I thought this is actually convenient way to get it while playing Krastorio! But alright.

It's mostly because both nests and spawner spitters have, well, "spawner" in their prototype. If this was a thing, all corpses would be lootable.
But from my experience it's not really a big deal to get a bit of biomass for the research and crafting of a biolab, afterwards it's just a spin-up