locale trouble when building packages

I select "Build Source Pakcage" in Rstudio, and Rstudio says:

==> devtools::document(roclets = c('rd', 'collate', 'namespace'))

During startup - Warning messages:
1: Setting LC_COLLATE failed, using "C" 
2: Setting LC_TIME failed, using "C" 
3: Setting LC_MESSAGES failed, using "C" 
4: Setting LC_MONETARY failed, using "C" 
Updating neopiR documentation

This only happens when running devtools. Not at starup, not at loading packages, nothing.

Doing R CMD BUILD also generates these locale messages.

What's going on? I'm on a Mac, I've done the

defaults write org.R-project.R force.LANG en_US.UTF-8

trick, and I set the locale environment variables in ~/.profile, ~/.bash_profile, and in ~/.Rprofile.

I'm running out of ideas.

Any and all hints and suggestions appreciated.

Thank you.