Why do I get this error when I install R on my computer ?

When I install R, I get this message.
When I want to use RStudio, many packages don't work, etc.

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_MESSAGES failed, using "C"
5: Setting LC_MONETARY failed, using "C"
[R.app GUI 1.73 (7892) x86_64-apple-darwin17.0]

WARNING: You're using a non-UTF8 locale, therefore only ASCII characters will work.
Please read R for Mac OS X FAQ (see Help) section 9 and adjust your system preferences accordingly.
[Workspace restored from /Users/Elena/.RData]
[History restored from /Users/Elena/.Rapp.history]

I highlighted the key part for you.
Utf8 and ascii are different ways computers can store text, so this all relates to the language settings of your computer.

Thank you. How do I change the language setting on my computer?