Merge #272: i18n: translate the whole interface into Japanese

Conflict: crates/ui-egui/src/i18n.rs: kept both module declarations (mod it; mod ja;)

crates/ui-egui/src/i18n.rs

@@ -5,6 +5,7 @@ use std::{collections::HashMap, sync::OnceLock};
 
 mod ar;
 mod it;
+mod ja;
 mod pt_br;
 mod uk;
 
@@ -2808,6 +2809,7 @@ fn column(lang: &str) -> Option<usize> {
 
 /// `s` in `lang` (English, or the string itself, when there's no translation).
 pub fn tr<'a>(lang: &str, s: &'a str) -> &'a str {
+    static JAPANESE: OnceLock<HashMap<&'static str, &'static str>> = OnceLock::new();
     static TRANSLATIONS: OnceLock<HashMap<&'static str, [&'static str; 5]>> = OnceLock::new();
     static ARABIC: OnceLock<HashMap<&'static str, &'static str>> = OnceLock::new();
     static UKRAINIAN: OnceLock<HashMap<&'static str, &'static str>> = OnceLock::new();
@@ -2816,6 +2818,13 @@ pub fn tr<'a>(lang: &str, s: &'a str) -> &'a str {
     if lang == "ar" {
         return ARABIC.get_or_init(|| ar::TABLE.iter().copied().collect()).get(s).copied().unwrap_or(s);
     }
+    // The Japanese table covers the whole interface; the shared table's Japanese column is the fallback
+    // for keys added there after it.
+    if lang == "ja"
+        && let Some(text) = JAPANESE.get_or_init(|| ja::TABLE.iter().copied().collect()).get(s).copied()
+    {
+        return text;
+    }
     if lang == "pt-br" {
         return PORTUGUESE_BR.get_or_init(|| pt_br::TABLE.iter().copied().collect()).get(s).copied().unwrap_or(s);
     }
@@ -2872,7 +2881,10 @@ mod tests {
     fn cached_lookup_preserves_every_translation_across_language_switches() {
         for (key, translations) in TABLE {
             for (lang, expected) in ["de", "fr", "es", "ja", "zh"].into_iter().zip(translations) {
-                assert_eq!(tr(lang, key), *expected, "{lang}: {key}");
+                // `ja::TABLE` translates the whole interface and wins over the shared Japanese column.
+                if lang != "ja" {
+                    assert_eq!(tr(lang, key), *expected, "{lang}: {key}");
+                }
             }
             assert_eq!(tr("", key), *key);
         }