That's an interesting workaround, unfortunately it doesn't allow to get back the initial mnemonic seed. Mnemonic shares are a bit long indeed but I could get with that. What I was looking for actually was the same tool as his Shamir39 tool, allowing to get shares into a mnemonic format from a BIP39 mnemonic but I understand it doesn't exist. It's sad they still haven't standardized a protocol allowing to do that. I don't want to rely on an isolated tool.