test: import 38 channelserver test files from v9.2.x-stable

Port test files from v9.2.x-stable branch to increase channelserver
coverage from 13.8% to 25.6% (556 tests passing).

Adapted all files to main's struct definitions: config import alias,
Airou/CatDefinition rename, packet field mismatches, Raviente struct
differences, and maxPlayers defaults. Removed tests referencing
production code not yet on main (Player, FestivalColour, etc.).
Excluded handlers_register_test.go (Raviente completely redesigned).

server/channelserver/sys_language_test.go

@@ -0,0 +1,94 @@
+package channelserver
+
+import (
+	"testing"
+
+	_config "erupe-ce/config"
+)
+
+func TestGetLangStrings_English(t *testing.T) {
+	server := &Server{
+		erupeConfig: &_config.Config{
+			Language: "en",
+		},
+	}
+
+	lang := getLangStrings(server)
+
+	if lang.language != "English" {
+		t.Errorf("language = %q, want %q", lang.language, "English")
+	}
+
+	// Verify key strings are not empty
+	if lang.cafe.reset == "" {
+		t.Error("cafe.reset should not be empty")
+	}
+	if lang.commands.disabled == "" {
+		t.Error("commands.disabled should not be empty")
+	}
+	if lang.commands.reload == "" {
+		t.Error("commands.reload should not be empty")
+	}
+	if lang.commands.ravi.noCommand == "" {
+		t.Error("commands.ravi.noCommand should not be empty")
+	}
+	if lang.guild.invite.title == "" {
+		t.Error("guild.invite.title should not be empty")
+	}
+}
+
+func TestGetLangStrings_Japanese(t *testing.T) {
+	server := &Server{
+		erupeConfig: &_config.Config{
+			Language: "jp",
+		},
+	}
+
+	lang := getLangStrings(server)
+
+	if lang.language != "日本語" {
+		t.Errorf("language = %q, want %q", lang.language, "日本語")
+	}
+
+	// Verify Japanese strings are different from English
+	enServer := &Server{
+		erupeConfig: &_config.Config{
+			Language: "en",
+		},
+	}
+	enLang := getLangStrings(enServer)
+
+	if lang.commands.reload == enLang.commands.reload {
+		t.Error("Japanese commands.reload should be different from English")
+	}
+}
+
+func TestGetLangStrings_DefaultToEnglish(t *testing.T) {
+	server := &Server{
+		erupeConfig: &_config.Config{
+			Language: "unknown_language",
+		},
+	}
+
+	lang := getLangStrings(server)
+
+	// Unknown language should default to English
+	if lang.language != "English" {
+		t.Errorf("Unknown language should default to English, got %q", lang.language)
+	}
+}
+
+func TestGetLangStrings_EmptyLanguage(t *testing.T) {
+	server := &Server{
+		erupeConfig: &_config.Config{
+			Language: "",
+		},
+	}
+
+	lang := getLangStrings(server)
+
+	// Empty language should default to English
+	if lang.language != "English" {
+		t.Errorf("Empty language should default to English, got %q", lang.language)
+	}
+}