I am sympathetic with non-English speakers wanting a native-language translation. But I think the interpreter should *always* emit the standard message and that any translation should be an addition, not a replacement. This would maintain discoverablity and help people learn the English version, not hinder it.

The real question to me is how deep in the interpreter such support should go. Third party shells can (and sometimes do) intercept tracebacks and reformat (and translate) as they wish. But there would be advantages and disadvanteges is adding the translation sooner.