Function miniextendr_assert_utf8_locale 

#[unsafe(no_mangle)]
pub extern "C" fn miniextendr_assert_utf8_locale()

Assert that R’s locale is UTF-8.

Called once from R_init_* (package init). Errors if the R session does not use UTF-8, since charsxp_to_str assumes all CHARSXP bytes are valid UTF-8.

Uses l10n_info()[["UTF-8"]] which is public R API.