desktop: Use system preferred language

Cargo.lock

@@ -3690,6 +3690,7 @@ dependencies = [
  "ruffle_render",
  "ruffle_render_wgpu",
  "ruffle_video_software",
+ "sys-locale",
  "tracing",
  "tracing-subscriber",
  "tracing-tracy",
@@ -4396,6 +4397,16 @@ dependencies = [
  "unicode-xid",
 ]
 
+[[package]]
+name = "sys-locale"
+version = "0.3.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ea0b9eefabb91675082b41eb94c3ecd91af7656caee3fb4961a07c0ec8c7ca6f"
+dependencies = [
+ "libc",
+ "windows-sys 0.45.0",
+]
+
 [[package]]
 name = "system-deps"
 version = "6.0.5"

desktop/Cargo.toml

@@ -28,6 +28,7 @@ anyhow = "1.0"
 bytemuck = "1.13.1"
 os_info = { version = "3", default-features = false }
 unic-langid = "0.9.1"
+sys-locale = "0.3.0"
 
 # Deliberately held back to match tracy client used by profiling crate
 tracing-tracy = { version = "=0.10.0", optional = true }

desktop/src/ui.rs

@@ -5,6 +5,7 @@ use ruffle_core::backend::ui::{
     FullscreenError, LanguageIdentifier, MouseCursor, UiBackend, US_ENGLISH,
 };
 use std::rc::Rc;
+use sys_locale::get_locale;
 use tracing::error;
 use winit::window::{Fullscreen, Window};
 
@@ -12,14 +13,20 @@ pub struct DesktopUiBackend {
     window: Rc<Window>,
     cursor_visible: bool,
     clipboard: Clipboard,
+    language: LanguageIdentifier,
 }
 
 impl DesktopUiBackend {
     pub fn new(window: Rc<Window>) -> Result<Self, Error> {
+        let preferred_language = get_locale();
+        let language = preferred_language
+            .and_then(|l| l.parse().ok())
+            .unwrap_or_else(|| US_ENGLISH.clone());
         Ok(Self {
             window,
             cursor_visible: true,
             clipboard: Clipboard::new().context("Couldn't get platform clipboard")?,
+            language,
         })
     }
 }
@@ -101,6 +108,6 @@ impl UiBackend for DesktopUiBackend {
     fn open_virtual_keyboard(&self) {}
 
     fn language(&self) -> &LanguageIdentifier {
-        &US_ENGLISH
+        &self.language
     }
 }