confusing error when a language does not exist

[gordonwoodhull]

If a language is configured but the package doesn't exist, you get

Error: session_init: Error in d(.session) : unused argument (.session)
collapse
R trace:
suppressWarnings(d(.session))
withCallingHandlers(expr, message = function(c) invokeRestart("muffleMessage"))
suppressMessages(suppressWarnings(d(.session)))
start.rcloud.common(...)
start.rcloud.gist(username = username, token = token, ...)
start.rcloud(...)
fun(...)
    at success (http://127.0.0.1:8080/js/rcloud_bundle.js:32:23)

Does not say which language module, or even the fact that a language module failed.