gtk: add localization support, take 3 (#6004)

This is my third (!) attempt at implementing localization support. By
leveraging GTK builder to do most of the `gettext` calls, I can avoid
the whole mess about missing symbols on non-glibc platforms.

Added some documentation too for contributors and translators, just for
good measure.

Supersedes #5214, resolves the GTK half of #2357

src/apprt/gtk/App.zig

@@ -39,6 +39,7 @@ const ConfigErrorsWindow = @import("ConfigErrorsWindow.zig");
 const ClipboardConfirmationWindow = @import("ClipboardConfirmationWindow.zig");
 const Split = @import("Split.zig");
 const c = @import("c.zig").c;
+const i18n = @import("i18n.zig");
 const version = @import("version.zig");
 const inspector = @import("inspector.zig");
 const key = @import("key.zig");
@@ -98,6 +99,11 @@ quit_timer: union(enum) {
 pub fn init(core_app: *CoreApp, opts: Options) !App {
     _ = opts;
 
+    // This can technically be placed *anywhere* because we don't have any
+    // localized log messages. It just has to be placed before any localized
+    // widgets are drawn.
+    try i18n.init(core_app.alloc);
+
     // Log our GTK version
     log.info("GTK version build={d}.{d}.{d} runtime={d}.{d}.{d}", .{
         c.GTK_MAJOR_VERSION,

src/apprt/gtk/Surface.zig

@@ -35,6 +35,7 @@ const gtk_key = @import("key.zig");
 const c = @import("c.zig").c;
 const Builder = @import("Builder.zig");
 const adwaita = @import("adwaita.zig");
+const i18n = @import("i18n.zig");
 
 const log = std.log.scoped(.gtk_surface);
 
@@ -1152,7 +1153,7 @@ pub fn setClipboardString(
             self.app.config.@"app-notifications".@"clipboard-copy")
         {
             if (self.container.window()) |window|
-                window.sendToast("Copied to clipboard");
+                window.sendToast(i18n._("Copied to clipboard"));
         }
         return;
     }

src/apprt/gtk/Window.zig

@@ -33,6 +33,7 @@ const TabView = @import("TabView.zig");
 const HeaderBar = @import("headerbar.zig");
 const version = @import("version.zig");
 const winproto = @import("winproto.zig");
+const i18n = @import("i18n.zig");
 
 const log = std.log.scoped(.gtk);
 
@@ -192,7 +193,7 @@ pub fn init(self: *Window, app: *App) !void {
 
     {
         const btn = c.gtk_menu_button_new();
-        c.gtk_widget_set_tooltip_text(btn, "Main Menu");
+        c.gtk_widget_set_tooltip_text(btn, i18n._("Main Menu"));
         c.gtk_menu_button_set_icon_name(@ptrCast(btn), "open-menu-symbolic");
         c.gtk_menu_button_set_popover(@ptrCast(btn), @ptrCast(@alignCast(self.titlebar_menu.asWidget())));
         _ = c.g_signal_connect_data(
@@ -212,7 +213,7 @@ pub fn init(self: *Window, app: *App) !void {
         const btn = switch (self.config.gtk_tabs_location) {
             .top, .bottom => btn: {
                 const btn = c.gtk_toggle_button_new();
-                c.gtk_widget_set_tooltip_text(btn, "View Open Tabs");
+                c.gtk_widget_set_tooltip_text(btn, i18n._("View Open Tabs"));
                 c.gtk_button_set_icon_name(@ptrCast(btn), "view-grid-symbolic");
                 _ = c.g_object_bind_property(
                     btn,
@@ -239,7 +240,7 @@ pub fn init(self: *Window, app: *App) !void {
 
     {
         const btn = c.gtk_button_new_from_icon_name("tab-new-symbolic");
-        c.gtk_widget_set_tooltip_text(btn, "New Tab");
+        c.gtk_widget_set_tooltip_text(btn, i18n._("New Tab"));
         _ = c.g_signal_connect_data(btn, "clicked", c.G_CALLBACK(&gtkTabNewClick), self, null, c.G_CONNECT_DEFAULT);
         self.headerbar.packStart(btn);
     }
@@ -257,7 +258,7 @@ pub fn init(self: *Window, app: *App) !void {
     // This is a really common issue where people build from source in debug and performance is really bad.
     if (comptime std.debug.runtime_safety) {
         const warning_box = c.gtk_box_new(c.GTK_ORIENTATION_VERTICAL, 0);
-        const warning_text = "⚠️ You're running a debug build of Ghostty! Performance will be degraded.";
+        const warning_text = i18n._("⚠️ You're running a debug build of Ghostty! Performance will be degraded.");
         if (adwaita.versionAtLeast(1, 3, 0)) {
             const banner = c.adw_banner_new(warning_text);
             c.adw_banner_set_revealed(@ptrCast(banner), 1);
@@ -674,10 +675,10 @@ pub fn focusCurrentTab(self: *Window) void {
 }
 
 pub fn onConfigReloaded(self: *Window) void {
-    self.sendToast("Reloaded the configuration");
+    self.sendToast(i18n._("Reloaded the configuration"));
 }
 
-pub fn sendToast(self: *Window, title: [:0]const u8) void {
+pub fn sendToast(self: *Window, title: [*:0]const u8) void {
     const toast = c.adw_toast_new(title);
     c.adw_toast_set_timeout(toast, 3);
     c.adw_toast_overlay_add_toast(@ptrCast(self.toast_overlay), toast);
@@ -930,7 +931,7 @@ fn gtkActionAbout(
             "application-name",
             name,
             "developer-name",
-            "Ghostty Developers",
+            i18n._("Ghostty Developers"),
             "application-icon",
             icon,
             "version",
@@ -949,7 +950,7 @@ fn gtkActionAbout(
             "logo-icon-name",
             icon,
             "title",
-            "About Ghostty",
+            i18n._("About Ghostty"),
             "version",
             build_config.version_string.ptr,
             "website",

src/apprt/gtk/i18n.zig

@@ -0,0 +1,37 @@
+//! I18n support for the GTK frontend based on gettext/libintl
+//!
+//! This is normally built into the C standard library for the *vast* majority
+//! of users who use glibc, but for musl users we fall back to the `gettext-tiny`
+//! stub implementation which provides all of the necessary interfaces.
+//! Musl users who do want to use localization should know what they need to do.
+
+const std = @import("std");
+const global = &@import("../../global.zig").state;
+const build_config = @import("../../build_config.zig");
+
+const log = std.log.scoped(.gtk_i18n);
+
+pub fn init(alloc: std.mem.Allocator) !void {
+    const resources_dir = global.resources_dir orelse {
+        log.warn("resource dir not found; not localizing", .{});
+        return;
+    };
+    const share_dir = std.fs.path.dirname(resources_dir) orelse {
+        log.warn("resource dir not placed in a share/ directory; not localizing", .{});
+        return;
+    };
+
+    const locale_dir = try std.fs.path.joinZ(alloc, &.{ share_dir, "locale" });
+    defer alloc.free(locale_dir);
+
+    // The only way these calls can fail is if we're out of memory
+    _ = bindtextdomain(build_config.bundle_id, locale_dir.ptr) orelse return error.OutOfMemory;
+    _ = textdomain(build_config.bundle_id) orelse return error.OutOfMemory;
+}
+
+// Manually include function definitions for the gettext functions
+// as libintl.h isn't always easily available (e.g. in musl)
+extern fn bindtextdomain(domainname: [*:0]const u8, dirname: [*:0]const u8) ?[*:0]const u8;
+extern fn textdomain(domainname: [*:0]const u8) ?[*:0]const u8;
+pub extern fn gettext(msgid: [*:0]const u8) [*:0]const u8;
+pub const _ = gettext;