feat(i18n): expose fallback language accessors

Co-Authored-By: Virgil <virgil@lethean.io>

i18n.go

@@ -54,6 +54,13 @@ func SetMode(m Mode) {
 	}
 }
 
+// SetFallback sets the fallback language for the default service.
+func SetFallback(lang string) {
+	if svc := Default(); svc != nil {
+		svc.SetFallback(lang)
+	}
+}
+
 // CurrentMode returns the current translation mode.
 func CurrentMode() Mode {
 	if svc := Default(); svc != nil {
@@ -62,6 +69,14 @@ func CurrentMode() Mode {
 	return ModeNormal
 }
 
+// CurrentFallback returns the current fallback language.
+func CurrentFallback() string {
+	if svc := Default(); svc != nil {
+		return svc.Fallback()
+	}
+	return "en"
+}
+
 // CurrentFormality returns the current default formality.
 func CurrentFormality() Formality {
 	if svc := Default(); svc != nil {

localise_test.go

@@ -120,6 +120,20 @@ func TestSetFormality_Good(t *testing.T) {
 	assert.Equal(t, FormalityNeutral, svc.Formality())
 }
 
+// --- Package-level SetFallback ---
+
+func TestSetFallback_Good(t *testing.T) {
+	svc, err := New()
+	require.NoError(t, err)
+	SetDefault(svc)
+
+	SetFallback("fr")
+	assert.Equal(t, "fr", svc.Fallback())
+
+	SetFallback("en")
+	assert.Equal(t, "en", svc.Fallback())
+}
+
 // --- Package-level CurrentFormality ---
 
 func TestCurrentFormality_Good(t *testing.T) {
@@ -133,6 +147,19 @@ func TestCurrentFormality_Good(t *testing.T) {
 	assert.Equal(t, FormalityFormal, CurrentFormality())
 }
 
+// --- Package-level CurrentFallback ---
+
+func TestCurrentFallback_Good(t *testing.T) {
+	svc, err := New()
+	require.NoError(t, err)
+	SetDefault(svc)
+
+	assert.Equal(t, "en", CurrentFallback())
+
+	SetFallback("fr")
+	assert.Equal(t, "fr", CurrentFallback())
+}
+
 // --- Package-level SetLocation ---
 
 func TestSetLocation_Good(t *testing.T) {

service.go

@@ -283,6 +283,12 @@ func (s *Service) SetMode(m Mode)           { s.mu.Lock(); s.mode = m; s.mu.Unlo
 func (s *Service) Mode() Mode               { s.mu.RLock(); defer s.mu.RUnlock(); return s.mode }
 func (s *Service) SetFormality(f Formality) { s.mu.Lock(); s.formality = f; s.mu.Unlock() }
 func (s *Service) Formality() Formality     { s.mu.RLock(); defer s.mu.RUnlock(); return s.formality }
+func (s *Service) SetFallback(lang string)  { s.mu.Lock(); s.fallbackLang = lang; s.mu.Unlock() }
+func (s *Service) Fallback() string {
+	s.mu.RLock()
+	defer s.mu.RUnlock()
+	return s.fallbackLang
+}
 
 func (s *Service) SetLocation(location string) {
 	s.mu.Lock()

service_test.go

@@ -228,6 +228,22 @@ func TestServiceModes(t *testing.T) {
 	svc.T("nonexistent.key")
 }
 
+func TestServiceFallback(t *testing.T) {
+	svc, err := New()
+	if err != nil {
+		t.Fatalf("New() failed: %v", err)
+	}
+
+	if svc.Fallback() != "en" {
+		t.Errorf("default Fallback() = %q, want en", svc.Fallback())
+	}
+
+	svc.SetFallback("fr")
+	if svc.Fallback() != "fr" {
+		t.Errorf("Fallback() = %q, want fr", svc.Fallback())
+	}
+}
+
 func TestServiceDebug(t *testing.T) {
 	svc, err := New()
 	if err != nil {