Continuing the discussion from Improve domain validation error to be more human readable:
Rational
The clients can show a human readable message when a domain is not valid (most of the case). But when the domain validation is done on the server side, the user only get a generic error message. It would give a better experience if the message could include the human readable message from the client.
Proposal
Before raising DomainValidationError, we take the first invalid record and evaluate with the domain_inversion method (the file tryton/common/domain_inversion.py could be copied from the client to the server as it depends only from Python stdlib) using the EvalEnvironment (which is compatible). The resulted inverted domain is send to the client as an extra parameter of the exception with the fields (from fields_get call). The client can use those extra parameters to instantiate a DomainParser and convert the domain into a string. This string will be appended to the error message.