DrRacket uses `LC_CTYPE` to set UI language

I’ve noticed that DrRacket presents me with German translations even though I have LANG=en_US.utf8 set. The issue seems to be that DrRacket is using the value of LC_CTYPE to determine the interface language.

This is reproducible using the following locale settings (NB this is locale(1) output, so quotation indicates inherited defaults):

LANG=en_US.utf8
LC_CTYPE=de_DE.utf8
LC_NUMERIC=de_DE.utf8
LC_TIME=de_DE.utf8
LC_COLLATE=de_DE.utf8
LC_MONETARY="en_US.utf8"
LC_MESSAGES="en_US.utf8"
LC_PAPER=de_DE.utf8
LC_NAME="en_US.utf8"
LC_ADDRESS="en_US.utf8"
LC_TELEPHONE="en_US.utf8"
LC_MEASUREMENT=de_DE.utf8
LC_IDENTIFICATION="en_US.utf8"
LC_ALL=

When unsetting LC_CTYPE or setting it to en_US.utf8, DrRacket starts up in English.

To determine interface language, (after checking LC_ALL) LC_MESSAGES should be looked up in the environment instead of LC_CTYPE, falling back to LANG when unset.

No file or test is named in the issue. Reproduce startup with the listed locale settings, then locate the entry point that selects DrRacket's interface language; done means LC_ALL and LC_MESSAGES are honored, with LANG as fallback, while LC_CTYPE alone does not change the UI language.