Add language-keyed i18n string initializers

docs/CHANGELOG.md

@@ -113,6 +113,9 @@
   the packaged systemd unit, and release preflight checks that metadata.
 - The Homebrew formula draft now defines a `brew services` entry that runs the
   installed `tnt` binary with state under `var/tnt`.
+- The i18n helper now supports language-keyed string initializers through
+  `I18N_STRING_MAP`, so future languages can be added incrementally without
+  changing every existing two-language string initializer.
 - Split UI-language parsing from localized text lookup: `src/i18n.c` now owns
   locale/code parsing, while `src/i18n_text.c` owns the table-driven text
   catalog with coverage checks for every message ID.

docs/Development-Guide.md

@@ -480,6 +480,10 @@ keys.
      fragments.
    - Keep placeholders visible and stable, for example `%s`, `%d`,
      `<user>`, and `<message>`.
+   - Use `I18N_STRING(en, zh)` for ordinary two-language entries.  Use
+     `I18N_STRING_MAP(I18N_EN(...), I18N_ZH(...))` when an entry needs
+     language-keyed initialization so future languages can be added without
+     changing every existing initializer.
    - Every new user-facing string needs tests for at least English fallback
      and Chinese output while this project has two UI languages.
 
@@ -488,7 +492,8 @@ keys.
 The current `src/i18n_text.c` implementation is a small-project translation
 table implemented in C, not a full gettext catalog.  It is acceptable for two
 languages because message lookup is already split from language parsing in
-`src/i18n.c`, but adding more languages should move toward catalog-like
+`src/i18n.c`, and localized strings can now be initialized by language key.
+Adding many more languages should still move toward external catalog-like
 storage instead of adding ad hoc branches for every locale.
 
 Relevant conventions:

include/i18n.h

@@ -7,8 +7,12 @@ typedef struct {
     const char *text[UI_LANG_COUNT];
 } i18n_string_t;
 
+#define I18N_LANG_TEXT(lang, value) [lang] = (value)
+#define I18N_EN(value) I18N_LANG_TEXT(UI_LANG_EN, value)
+#define I18N_ZH(value) I18N_LANG_TEXT(UI_LANG_ZH, value)
+#define I18N_STRING_MAP(...) {{ __VA_ARGS__ }}
 #define I18N_STRING(en_text, zh_text) \
-    {{ [UI_LANG_EN] = (en_text), [UI_LANG_ZH] = (zh_text) }}
+    I18N_STRING_MAP(I18N_EN(en_text), I18N_ZH(zh_text))
 
 typedef enum {
     I18N_USERNAME_PROMPT,

tests/unit/test_i18n.c

@@ -80,10 +80,21 @@ TEST(default_uses_locale_when_no_tnt_lang) {
 
 TEST(text_lookup_matches_language) {
     i18n_string_t sample = I18N_STRING("fallback", "替代");
+    i18n_string_t mapped = I18N_STRING_MAP(
+        I18N_EN("mapped fallback"),
+        I18N_ZH("映射替代")
+    );
+    i18n_string_t english_only = I18N_STRING_MAP(
+        I18N_EN("english only")
+    );
 
     assert(strcmp(i18n_string(sample, UI_LANG_EN), "fallback") == 0);
     assert(strcmp(i18n_string(sample, UI_LANG_ZH), "替代") == 0);
     assert(strcmp(i18n_string(sample, (ui_lang_t)99), "fallback") == 0);
+    assert(strcmp(i18n_string(mapped, UI_LANG_EN), "mapped fallback") == 0);
+    assert(strcmp(i18n_string(mapped, UI_LANG_ZH), "映射替代") == 0);
+    assert(strcmp(i18n_string(english_only, UI_LANG_ZH),
+                  "english only") == 0);
 
     assert(strstr(i18n_text(UI_LANG_EN, I18N_USERNAME_PROMPT),
                   "display name") != NULL);