Cannot set locale in Rstudio

## --- The problem: ---

I'm trying to run Rstudio, but whenever I start up I see these messages:

During startup - Warning messages:
1: Setting LC_CTYPE failed, using "C" 
2: Setting LC_COLLATE failed, using "C" 
3: Setting LC_TIME failed, using "C" 
4: Setting LC_MONETARY failed, using "C" 

Which I guess I could ignore, but when I try to install packages I get this :

tar: Failed to set default locale

so there's lots of things that I actually can't do now and to use R I guess I need to set the locale.

# --- What I've tried: ---

Based on suggestions I've seen in other forums, I've tried the following:

(from within R)

> Sys.setlocale("LC_ALL","English")

(from terminal)

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

(added to .bash_profile/.bashrc/pretty much anything else I could think of )

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

None of the above resolved the problem, nor made any difference as far as I could tell.

# --- More info: ---

I'm using a macbook M1, OS Monterey. I used to use `R` via homebrew but as I have heard there are issues with that route, I've uninstalled that and installed system `R` from cran (this doesn't appear to make any difference) From the session, I get the following locale info:

> Sys.getlocale()
[1] "C/C/C/C/C/en_US.UTF-8"

I have no idea what's with all the extra `C/`'s , but I'd like to stick to US english UTF-8.

> sessionInfo()
R version 4.2.3 (2023-03-15)
Platform: aarch64-apple-darwin20 (64-bit)
Running under: macOS Monterey 12.6.1

Matrix products: default
LAPACK: /Library/Frameworks/R.framework/Versions/4.2-arm64/Resources/lib/libRlapack.dylib

locale:
[1] C/C/C/C/C/en_US.UTF-8

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base     

loaded via a namespace (and not attached):
[1] compiler_4.2.3 tools_4.2.3  

Any help would be much appreciated. I've never had any of these issues on linux machines, and have no idea where this is coming from.