Installing R on Mac - Warning messages: Setting LC_CTYPE failed, using "C"

1. Open Terminal
2. Write or paste in: defaults write org.R-project.R force.LANG en_US.UTF-8
3. Close Terminal (including any RStudio window)
4. Start R

For someone runs R in a docker environment (under root), try to run R with below command,

LC_ALL=C.UTF-8 R
# instead of just `R`

Setting locales in terminal resolved the issue for me. Open the terminal and

1. Check if locale settings are missing

   > locale
   LANG=
   LC_COLLATE="C"
   LC_CTYPE="UTF-8"
   LC_MESSAGES="C"
   LC_MONETARY="C"
   LC_NUMERIC="C"
   LC_TIME="C"
   LC_ALL=
   

2. Edit ~/.profile or ~/.bashrc

   export LANG=en_US.UTF-8
   export LC_ALL=en_US.UTF-8
   

3. Run . ~/.profile or . ~/.bashrc to read from the file.

4. Open a new terminal window and check that the locales are properly set

   > locale
   LANG="en_US.UTF-8"
   LC_COLLATE="en_US.UTF-8"
   LC_CTYPE="en_US.UTF-8"
   LC_MESSAGES="en_US.UTF-8"
   LC_MONETARY="en_US.UTF-8"
   LC_NUMERIC="en_US.UTF-8"
   LC_TIME="en_US.UTF-8"
   LC_ALL="en_US.UTF-8"