refactor: make UI localization extensible and integrate upstream

crates/ui-egui/src/fonts.rs

@@ -1,8 +1,10 @@
 //! System font loading and fallback setup for multi-language (CJK/Japanese) support.
 
+#[cfg(not(target_arch = "wasm32"))]
 use std::sync::Arc;
 
 /// Candidate font paths to look for on different operating systems.
+#[cfg(not(target_arch = "wasm32"))]
 const FONT_CANDIDATES: &[&str] = &[
     // Windows
     "C:\\Windows\\Fonts\\meiryo.ttc",
@@ -11,6 +13,7 @@ const FONT_CANDIDATES: &[&str] = &[
     "C:\\Windows\\Fonts\\msgothic.ttc",
     "C:\\Windows\\Fonts\\BIZ-UDGothicR.ttc",
     // macOS
+    "/System/Library/Fonts/ヒラギノ角ゴシック W3.ttc",
     "/System/Library/Fonts/Hiragino Sans GB.ttc",
     "/System/Library/Fonts/PingFang.ttc",
     "/Library/Fonts/Arial Unicode.ttf",
@@ -22,10 +25,13 @@ const FONT_CANDIDATES: &[&str] = &[
 ];
 
 /// Configure font definitions with system CJK fallback if available.
+#[cfg(not(target_arch = "wasm32"))]
 pub fn setup_fonts(ctx: &egui::Context) {
     let mut font_bytes: Option<Vec<u8>> = None;
     for path in FONT_CANDIDATES {
-        if let Ok(bytes) = std::fs::read(path) {
+        if let Ok(bytes) = std::fs::read(path)
+            && ttf_parser::Face::parse(&bytes, 0).is_ok()
+        {
             font_bytes = Some(bytes);
             break;
         }
@@ -44,3 +50,7 @@ pub fn setup_fonts(ctx: &egui::Context) {
 
     ctx.set_fonts(fonts);
 }
+
+/// Browsers cannot read system font files. A web host can supply licensed fonts through egui.
+#[cfg(target_arch = "wasm32")]
+pub fn setup_fonts(_ctx: &egui::Context) {}