How to fix 'tar: Failed to set default locale' error?
Step 1 (In R Console)
system('defaults write org.R-project.R force.LANG en_US.UTF-8')
Step 2: Restart R
Source: http://cran.r-project.org/bin/macosx/RMacOSX-FAQ.html#Internationalization-of-the-R_002eapp