Internationalized Domain Names (IDNs) Explained

## The Internet Was Built in English — and Then the World Showed Up When the domain name system was designed in the 1980s, it was built around the ASCII character set: the 26 letters of the English alphabet, the digits 0–9, and the hyphen. For the first two decades of the web, every domain name had to be expressed in those characters alone. That was a practical choice for the time, but it created a fundamental inequity: the billions of people who communicate in Arabic, Chinese, Cyrillic, Hindi, Japanese, Korean, Thai, and hundreds of other scripts could not register domain names in their own writing systems. Their websites could serve content in any language, but the address bar still had to display English-script characters. Internationalized Domain Names — IDNs — are the internet's answer to that problem. They allow domain names to be registered and displayed in any language script supported by the Unicode standard. Today, you can register domains in Russian Cyrillic, Arabic, Chinese, Japanese, and dozens of other scripts, and they will work in all modern browsers. Understanding how IDNs work, where they are supported, and what pitfalls to watch for is essential for anyone building an international web presence or targeting non-English-speaking audiences. ## What Is Unicode and Why Does It Matter for Domains? Unicode is the universal character encoding standard that assigns a unique number (called a code point) to every character in every writing system used by humans. As of Unicode 15.0, the standard covers more than 149,000 characters across 161 scripts. Before Unicode, different regions used incompatible character encodings — a document written in one encoding would display as gibberish on a system configured for another. Unicode solved that by creating one unified system. The DNS (Domain Name System), however, was built before Unicode existed, and its underlying protocol still operates on ASCII bytes. When you type an IDN into your browser, the browser does not actually send the Unicode characters to the DNS. Instead, it silently converts them into an ASCII-compatible encoding first. That encoding is called Punycode. ## Punycode: The ASCII Bridge Punycode is an algorithm defined in RFC 3492 that encodes Unicode strings as ASCII strings. The process works as follows: 1. Any ASCII characters in the label are kept as-is. 2. All non-ASCII Unicode characters are appended in a compact encoded form. 3. The label is prefixed with `xn--` to signal to DNS resolvers that this is a Punycode-encoded IDN. The prefix `xn--` is the visible marker that a domain label contains Punycode encoding. You will sometimes see these raw Punycode forms in DNS records, SSL certificates, and older browser address bars that do not support Unicode display. Some examples: | Unicode form | Punycode / ACE form | |---|---| | `münchen.de` | `xn--mnchen-3ya.de` | | `例子.com` | `xn--fsq270a.com` | | `مثال.com` | `xn--mgbh0fb.com` | The conversion is fully automatic in modern browsers and operating systems. When a user types an IDN into Chrome or Firefox, the browser resolves the Punycode form without the user ever seeing it. The user experience is seamless — unless something goes wrong, which we will discuss shortly. ## IDN TLDs: Country Codes and Generic Extensions in Local Scripts IDN support extends to the TLD (Top-Level Domain) level as well as the second-level domain. ICANN has delegated IDN country-code TLDs for dozens of countries, allowing both the domain name and the extension to be written in a non-ASCII script. Some notable IDN ccTLDs include: | Script | Territory | IDN ccTLD | |---|---|---| | Arabic | Saudi Arabia | .السعودية | | Arabic | Egypt | .مصر | | Cyrillic | Russia | .рф | | Chinese (simplified) | China | .中国 | | Chinese (traditional) | Taiwan | .台灣 | | Korean | South Korea | .한국 | | Japanese | Japan | .日本 | | Hindi | India | .भारत | | Thai | Thailand | .ไทย | There are also IDN generic TLDs and various script-specific proposed extensions, though generic IDN TLDs have seen slower adoption than IDN ccTLDs. ## Registering an IDN: What You Need to Know ### Registrar Support Not all registrars support IDN registration. Major global registrars like GoDaddy, Namecheap, and Name.com offer IDN registration for popular scripts and TLDs, but support varies by script and TLD. Before attempting to register an IDN, confirm that your chosen registrar supports both the script you want to use and the specific TLD. Use WHOIS Lookup Tool to verify whether an IDN is already registered. Many WHOIS tools display both the Unicode form and the Punycode ACE form of the domain. ### Language and Script Restrictions ICANN requires registries to enforce language tables — approved lists of characters that may appear in domain labels for a given TLD. This prevents mixing characters from different scripts (e.g., a mix of Latin and Cyrillic that looks identical but is not) in a single label. The `.рф` (Russian) TLD, for example, only permits Cyrillic characters. You cannot register a `.рф` domain that mixes Cyrillic and Latin characters. These restrictions exist to prevent homograph attacks (see below). ### DNS Configuration Once registered, an IDN functions like any other domain from a DNS perspective. Your Domain Registrar stores the Punycode ACE form in the DNS (Domain Name System), and you configure DNS records using that ACE form. Your web server, SSL certificate, and email configuration all reference the Punycode form. Most modern control panels handle this conversion transparently. ### SSL/TLS Certificates SSL/TLS Certificate certificates for IDNs are issued for the ACE (Punycode) form of the domain. Certificate Authorities validate the ACE form, not the Unicode display form. Modern browsers display the Unicode form in the address bar for trusted certificates, but the underlying certificate is for the Punycode string. This works seamlessly for end users but is worth understanding if you manage certificates manually. ## The Homograph Attack Problem The most significant security concern with IDNs is the **homograph attack** (also called a homoglyph attack or IDN spoofing). This exploit takes advantage of the visual similarity between characters in different Unicode scripts. For example: - The Latin letter "a" (U+0061) and the Cyrillic letter "а" (U+0430) look identical in most fonts. - The Latin letter "o" (U+006F) and the Greek letter "ο" (U+03BF) are visually indistinguishable. A malicious actor could register a domain that *looks* exactly like a well-known site but contains Cyrillic or Greek characters, and use it for phishing. Because the Unicode form displays in the address bar, a careful user might not notice the difference. Browser vendors and registries have implemented several countermeasures: - **Punycode fallback:** Modern browsers display the Punycode form for domains that mix scripts or contain characters from scripts that are not universally trusted. - **Registry language tables:** IDN registries restrict registration to single-script labels, preventing the most obvious cross-script homographs. - **Browser heuristics:** Browsers flag IDNs that look like known domains but differ at the Unicode level. As a registrant, the practical lesson is: always verify the Punycode form of any IDN you visit or register. Use WHOIS Lookup Tool or your browser's developer tools to inspect the actual DNS name being resolved. ## Business Use Cases for IDNs ### Local Language Branding For businesses primarily serving a non-English-speaking audience, an IDN can signal cultural commitment and local relevance. A Chinese e-commerce site with a fully Chinese domain communicates local identity in a way that a transliterated ASCII domain cannot. This matters especially in markets where customers associate Latin-script domains with foreign or impersonal brands. ### Protecting Your Brand in Local Scripts If your brand name has a natural transcription or translation in another language, registering the IDN form is a defensive brand protection measure. Large consumer brands have registered Cyrillic, Arabic, Chinese, and Japanese IDN variations of their trademarks to prevent squatters from registering confusingly similar IDNs for phishing or counterfeit goods. ### Email in Local Scripts IDN support has been extended to email addresses through the EAI (Email Address Internationalization) standard. Internationalized email addresses are technically valid, but EAI adoption is still limited — many email servers and clients do not yet support them. If you plan to use IDN-based email, test thoroughly across your target audience's email clients. ## IDNs and SEO From a pure SEO standpoint, IDN domains function like any other domain. Google indexes and ranks IDN pages based on the same signals — content quality, backlinks, page experience — it applies to ASCII domains. The Punycode form is what appears in Google's index; the Unicode form is what users see in search results and browser bars. A few practical notes: - In markets where search engines heavily favor local-script content, an IDN with high-frequency local keywords in the domain may have a marginal directional advantage, similar to exact-match domains in English. - If you operate multilingual sites, coordinate your IDN strategy with your hreflang and FQDN (Fully Qualified Domain Name) configuration to avoid sending conflicting language signals. - Inbound links to an IDN use either the Unicode or Punycode form; both resolve to the same domain and count equally. ## Should You Register an IDN? Ask yourself: 1. Is your primary audience more comfortable in a non-ASCII script? 2. Does your brand name have a meaningful, pronounceable form in that script? 3. Does the target ccTLD (Country-Code Top-Level Domain) or gTLD (Generic Top-Level Domain) have meaningful market recognition in your audience? 4. Can your registrar, hosting provider, and certificate authority support the IDN fully? If the answers are yes, an IDN can be a genuine branding and accessibility win. If your audience is globally mixed or primarily English-speaking, the complexity rarely justifies the benefit. Use TLD Finder to explore available IDN TLDs for your target market, and TLD Comparison Tool to compare the trust and adoption levels of IDN versus ASCII options. ## Key Takeaways - IDNs allow domain names in any Unicode script — Arabic, Chinese, Cyrillic, Japanese, Thai, and more. - The DNS (Domain Name System) still operates in ASCII; Punycode silently converts Unicode labels into the `xn--` ACE form for DNS resolution. - ICANN has delegated IDN ccTLDs for dozens of countries, allowing fully script-native domain names. - Language tables restrict IDN registrations to single-script labels, reducing but not eliminating homograph attack risk. - SSL/TLS Certificate certificates are issued for the Punycode ACE form; browsers display the Unicode form to users. - For non-English-speaking markets, IDNs offer meaningful branding advantages; for mixed or global audiences, ASCII domains remain the safer choice. For related reading, see Numbers and Hyphens in Domain Names on character choices in ASCII domains, and domain-name-branding on brand alignment in TLD selection.