feat: determine system locale to use in locale-aware unicode sorting

Prerequisite to an implementation of #1006[1]
following the example of tidy's `sort_carefully`[2].

[1]: #1006
[2]: https://github.com/sts10/tidy/blob/main/src/list_manipulations.rs#L24

Cargo.toml

@@ -74,6 +74,7 @@ name = "eza"
 nu-ansi-term = "0.50.0"
 chrono = { version = "0.4.34", default-features = false, features = ["clock"] }
 glob = "0.3"
+icu_locid = "1.5.0"
 libc = "0.2"
 locale = "0.2"
 log = "0.4"

src/main.rs

@@ -81,6 +81,25 @@ fn main() {
                 }
             }
 
+            let lang = if let Ok(lang) = std::env::var("LANG") {
+                // Split e.g. "en_US.UTF-8", extracting "en_US".
+                match lang.split_once('.') {
+                    Some((lang, _)) => lang.to_owned(),
+                    None => lang,
+                }
+            } else {
+                // Fall back to "en_US" if the `LANG` environment variable is not set.
+                warn!("`LANG` is not set. Falling back to 'en_US'.");
+                String::from("en_US")
+            };
+
+            let locale: icu_locid::Locale = if let Ok(locale) = lang.parse() {
+                locale
+            } else {
+                warn!("Your locale '{lang}' could not be parsed. Falling back to 'en_US'.");
+                "en_US".parse().unwrap()
+            };
+
             let git = git_options(&options, &input_paths);
             let writer = io::stdout();
             let git_repos = git_repos(&options, &input_paths);
@@ -91,6 +110,7 @@ fn main() {
                 options,
                 writer,
                 input_paths,
+                locale,
                 theme,
                 console_width,
                 git,
@@ -149,6 +169,9 @@ pub struct Exa<'args> {
     /// names (anything that isn’t an option).
     pub input_paths: Vec<&'args OsStr>,
 
+    /// The system locale, used for locale-aware unicode string sorting.
+    pub locale: icu_locid::Locale,
+
     /// The theme that has been configured from the command-line options and
     /// environment variables. If colours are disabled, this is a theme with
     /// every style set to the default.