Fix Unicode title casing and slug normalization

src/transforms/case.test.ts

@@ -0,0 +1,19 @@
+import { describe, it, expect } from "vitest";
+import { latinize, slugify, toTitleCase } from "./case";
+
+describe("unicode case handling", () => {
+	it("should title-case words with Polish diacritics without mangling letters", () => {
+		const input = "Weryfikacja reżimu podatkowego";
+		expect(toTitleCase(input)).toBe("Weryfikacja Reżimu Podatkowego");
+	});
+
+	it("should strip combining marks while preserving letters, numbers, whitespace, and underscores", () => {
+		expect(latinize("Reżym 123_test")).toBe("Rezym 123_test");
+	});
+
+	it("should slugify Unicode words into a URL-friendly string", () => {
+		expect(slugify("Weryfikacja reżimu podatkowego")).toBe(
+			"weryfikacja-rezimu-podatkowego"
+		);
+	});
+});

src/transforms/case.ts

@@ -79,7 +79,7 @@ export function toDotCase(text: string): string {
 export function toTitleCase(text: string): string {
 	return perLine(text, (line) =>
 		line.replace(
-			/\b\w+/g,
+			/[\p{L}\p{N}]+/gu,
 			(w) => w.charAt(0).toUpperCase() + w.slice(1).toLowerCase()
 		)
 	);
@@ -135,7 +135,9 @@ export function reverseLines(text: string): string {
 
 /** Removes diacritic marks — e.g. "café" → "cafe", "Ñoño" → "Nono" */
 export function latinize(text: string): string {
-	return text.normalize("NFD").replace(/[\u0300-\u036f]/g, "");
+	return text
+		.normalize("NFD")
+		.replace(/[^\p{L}\p{N}_\s]+/gu, "");
 }
 
 /** URL-friendly slug: lowercase, ASCII, spaces→dashes */