Not able to translate the document message sendaslinkexternal__v.
The document message is translated based on the language settings of the Vault if the recipient is not a user in vault.
If the external user does not have an account in Vault, the notification will translate to the base language of the vault. As the notification is being sent to an email address not in vault, vault does not know the language of the recipient,therefore, the message is sent in the Vault's base language.
- Vault Documentation: Vault Help