When you have a key marked as "removed" in lang/deprecated.json, it doesn't just deprecate it makes it entirely untranslatable for all packs everywhere. And it does this silently, which is not very friendly.

In my resource pack, I overrode your "wither" (and other) painting with another one by another artist. So I added my own lang/en_us.json that include the key "painting.minecraft.wither.author" with the artist for that painting. Mysteriously this did not translate. It took me some time (and filing a bug that got marked "invalid", MC-278445) to figure out that this was because of deprecated.json removing that key.

First, throwing away data silently is just wrong. You should at least log a warning when encountering a deprecated key.

Second, I think deprecation should only apply to the pack itself. Or alternatively, you could just remove those key/value pairs from all your files, which would give the same result for your resource packs, but allow me to provide such a value if relevant, which it is here. (Poor Josef Albers is not getting the credit from me that he deserves.)