Fix unicode capitalization in plural forms

grammar.go

@@ -371,10 +371,7 @@ func Pluralize(noun string, count int) string {
 		}
 		lower := core.Lower(noun)
 		if form := getNounForm(currentLangForGrammar(), lower, "one"); form != "" {
-			if unicode.IsUpper(rune(noun[0])) && len(form) > 0 {
-				return core.Upper(string(form[0])) + form[1:]
-			}
-			return form
+			return preserveInitialCapitalization(noun, form)
 		}
 		return noun
 	}
@@ -389,16 +386,10 @@ func PluralForm(noun string) string {
 	}
 	lower := core.Lower(noun)
 	if form := getNounForm(currentLangForGrammar(), lower, "other"); form != "" {
-		if unicode.IsUpper(rune(noun[0])) && len(form) > 0 {
-			return core.Upper(string(form[0])) + form[1:]
-		}
-		return form
+		return preserveInitialCapitalization(noun, form)
 	}
 	if plural, ok := irregularNouns[lower]; ok {
-		if unicode.IsUpper(rune(noun[0])) {
-			return core.Upper(string(plural[0])) + plural[1:]
-		}
-		return plural
+		return preserveInitialCapitalization(noun, plural)
 	}
 	return applyRegularPlural(noun)
 }
@@ -675,6 +666,22 @@ func isInitialism(word string) bool {
 	return hasLetter
 }
 
+func preserveInitialCapitalization(original, form string) string {
+	if original == "" || form == "" {
+		return form
+	}
+	originalRunes := []rune(original)
+	formRunes := []rune(form)
+	if len(originalRunes) == 0 || len(formRunes) == 0 {
+		return form
+	}
+	if !unicode.IsUpper(originalRunes[0]) {
+		return form
+	}
+	formRunes[0] = unicode.ToUpper(formRunes[0])
+	return string(formRunes)
+}
+
 func initialismUsesVowelSound(word string) bool {
 	if word == "" {
 		return false

grammar_test.go

@@ -263,6 +263,33 @@ func TestPluralize_UsesLocaleSingularOverride(t *testing.T) {
 	}
 }
 
+func TestPluralize_PreservesUnicodeCapitalization(t *testing.T) {
+	prev := Default()
+	t.Cleanup(func() {
+		SetDefault(prev)
+	})
+
+	svc, err := New()
+	if err != nil {
+		t.Fatalf("New() failed: %v", err)
+	}
+	SetDefault(svc)
+
+	if err := SetLanguage("fr"); err != nil {
+		t.Fatalf("SetLanguage(fr) failed: %v", err)
+	}
+
+	if got, want := Pluralize("Élément", 1), "Élément"; got != want {
+		t.Fatalf("Pluralize(%q, 1) = %q, want %q", "Élément", got, want)
+	}
+	if got, want := Pluralize("Élément", 2), "Éléments"; got != want {
+		t.Fatalf("Pluralize(%q, 2) = %q, want %q", "Élément", got, want)
+	}
+	if got, want := PluralForm("Élément"), "Éléments"; got != want {
+		t.Fatalf("PluralForm(%q) = %q, want %q", "Élément", got, want)
+	}
+}
+
 func TestPluralForm(t *testing.T) {
 	svc, err := New()
 	if err != nil {