Localize date strings

Mostly closes: #103

Analogous to my other patches that localize date strings (e.g.
pop-os/cosmic-files#277).

The "password:" prompt is not localized in this patch because PAM should
yield translated strings on its own. This needs further investigation.

src/localize.rs

@@ -1,6 +1,9 @@
 // SPDX-License-Identifier: GPL-3.0-only
 
-use std::sync::OnceLock;
+use std::{
+    str::FromStr,
+    sync::{LazyLock, OnceLock},
+};
 
 use i18n_embed::{
     fluent::{fluent_language_loader, FluentLanguageLoader},
@@ -13,6 +16,19 @@ use rust_embed::RustEmbed;
 struct Localizations;
 
 pub static LANGUAGE_LOADER: OnceLock<FluentLanguageLoader> = OnceLock::new();
+pub static LANGUAGE_CHRONO: LazyLock<chrono::Locale> = LazyLock::new(|| {
+    std::env::var("LC_TIME")
+        .ok()
+        .or_else(|| std::env::var("LANG").ok())
+        .and_then(|locale_full| {
+            // Split LANG because it may be set to a locale such as en_US.UTF8
+            locale_full
+                .split('.')
+                .next()
+                .and_then(|locale| chrono::Locale::from_str(locale).ok())
+        })
+        .unwrap_or(chrono::Locale::en_US)
+});
 
 #[macro_export]
 macro_rules! fl {