Don't quote Unicode member names in type signatures

CHANGELOG.md

@@ -7,6 +7,7 @@ title: Changelog
 ### Bug Fixes
 
 - Anchor links in the mobile hamburger menu now correctly scroll to their target, #3049.
+- Member names containing non-ASCII characters are no longer rendered as quoted strings in type signatures if they are valid identifiers.
 
 ## v0.28.20 (2026-07-05)
 

src/lib/output/formatter.tsx

@@ -16,12 +16,35 @@ import {
 } from "#models";
 import { aggregate, assertNever, JSX } from "#utils";
 import { ok } from "assert";
+import ts from "typescript";
 import type { Router } from "./index.js";
 import { getKindClass, getUniquePath, stringify } from "./themes/lib.js";
 
 // Non breaking space
 const INDENT = "\u00A0\u00A0\u00A0\u00A0";
 
+function isIdentifierText(name: string): boolean {
+    let codePoint = name.codePointAt(0);
+    if (
+        codePoint === undefined ||
+        !ts.isIdentifierStart(codePoint, ts.ScriptTarget.Latest)
+    ) {
+        return false;
+    }
+
+    for (
+        let offset = codePoint > 0xffff ? 2 : 1;
+        offset < name.length;
+        offset += codePoint > 0xffff ? 2 : 1
+    ) {
+        codePoint = name.codePointAt(offset)!;
+        if (!ts.isIdentifierPart(codePoint, ts.ScriptTarget.Latest)) {
+            return false;
+        }
+    }
+    return true;
+}
+
 export type FormatterNode =
     | { type: "text"; content: string }
     | { type: "element"; content: JSX.Element; length: number }
@@ -1143,7 +1166,7 @@ export class FormattedCodeBuilder {
         reflection: Reflection,
         options: { topLevelLinks?: boolean },
     ): FormatterNode {
-        const entityName = /^[A-Z_$][\w$]*$/i.test(reflection.name)
+        const entityName = isIdentifierText(reflection.name)
             ? reflection.name
             : JSON.stringify(reflection.name);
 

src/test/output/formatter.test.ts

@@ -621,6 +621,83 @@ describe("Formatter", () => {
         );
     });
 
+    it("Does not quote non-ASCII member names which are valid identifiers", () => {
+        const refl = new DeclarationReflection(
+            "__type",
+            ReflectionKind.TypeLiteral,
+        );
+        for (const name of ["café", "Größe", "日本語", "имя", "zw\u200Cnj"]) {
+            const child = new DeclarationReflection(
+                name,
+                ReflectionKind.Property,
+                refl,
+            );
+            child.type = new IntrinsicType("string");
+            refl.addChild(child);
+        }
+
+        const type = new ReflectionType(refl);
+        const text = renderElementToText(renderType(type));
+        equal(
+            text,
+            "{ café: string; Größe: string; 日本語: string; имя: string; zw\u200Cnj: string }",
+        );
+
+        const textWrap = renderElementToText(renderType(type, 0));
+        equal(
+            textWrap,
+            dedent(`
+                {
+                    café: string;
+                    Größe: string;
+                    日本語: string;
+                    имя: string;
+                    zw\u200Cnj: string;
+                }
+            `),
+        );
+    });
+
+    it("Quotes member names which are not valid identifiers", () => {
+        const refl = new DeclarationReflection(
+            "__type",
+            ReflectionKind.TypeLiteral,
+        );
+        for (const name of ["[iterator]", "0", "a-b", "with space"]) {
+            const child = new DeclarationReflection(
+                name,
+                ReflectionKind.Property,
+                refl,
+            );
+            child.type = new IntrinsicType("string");
+            refl.addChild(child);
+        }
+
+        const type = new ReflectionType(refl);
+        const text = renderElementToText(renderType(type));
+        equal(
+            text,
+            `{ "[iterator]": string; "0": string; "a-b": string; "with space": string }`,
+        );
+    });
+
+    it("Uses TypeScript's identifier table", () => {
+        const refl = new DeclarationReflection(
+            "__type",
+            ReflectionKind.TypeLiteral,
+        );
+        const child = new DeclarationReflection(
+            "\u088F",
+            ReflectionKind.Property,
+            refl,
+        );
+        child.type = new IntrinsicType("string");
+        refl.addChild(child);
+
+        const type = new ReflectionType(refl);
+        equal(renderElementToText(renderType(type)), `{ "\u088F": string }`);
+    });
+
     it("Handles rest types", () => {
         const type = new RestType(new LiteralType("x"));
         const text = renderElementToText(renderType(type));