Suatu halaman HTML harus menyertakan atribut lang di dalam tag, untuk mendeklarasikan bahasa yang digunakan dalam halaman Web. Ini dimaksudkan untuk membantu mesin pencari dan browser:
<html lang="en"> ... </html>
Untuk bahasa Indonesia menggunakan id
<html lang="id"> ... </html>
Dalam XHTML, bahasa dideklarasikan di dalam tag sebagai berikut:
<html xmlns="http://www.w3.org/1999/xhtml" lang="en" xml:lang="en"> ... </html>
Kode Bahasa ISO 639-1
| Bahasa | Kode ISO |
|---|---|
| Abkhazian | ab |
| Afar | aa |
| Afrikaans | af |
| Akan | ak |
| Albanian | sq |
| Amharic | am |
| Arabic | ar |
| Aragonese | an |
| Armenian | hy |
| Assamese | as |
| Avaric | av |
| Avestan | ae |
| Aymara | ay |
| Azerbaijani | az |
| Bambara | bm |
| Bashkir | ba |
| Basque | eu |
| Belarusian | be |
| Bengali (Bangla) | bn |
| Bihari | bh |
| Bislama | bi |
| Bosnian | bs |
| Breton | br |
| Bulgarian | bg |
| Burmese | my |
| Catalan | ca |
| Chamorro | ch |
| Chechen | ce |
| Chichewa, Chewa, Nyanja | ny |
| Chinese | zh |
| Chinese (Simplified) | zh-Hans |
| Chinese (Traditional) | zh-Hant |
| Chuvash | cv |
| Cornish | kw |
| Corsican | co |
| Cree | cr |
| Croatian | hr |
| Czech | cs |
| Danish | da |
| Divehi, Dhivehi, Maldivian | dv |
| Dutch | nl |
| Dzongkha | dz |
| English | en |
| Esperanto | eo |
| Estonian | et |
| Ewe | ee |
| Faroese | fo |
| Fijian | fj |
| Finnish | fi |
| French | fr |
| Fula, Fulah, Pulaar, Pular | ff |
| Galician | gl |
| Gaelic (Scottish) | gd |
| Gaelic (Manx) | gv |
| Georgian | ka |
| German | de |
| Greek | el |
| Greenlandic | kl |
| Guarani | gn |
| Gujarati | gu |
| Haitian Creole | ht |
| Hausa | ha |
| Hebrew | he |
| Herero | hz |
| Hindi | hi |
| Hiri Motu | ho |
| Hungarian | hu |
| Icelandic | is |
| Ido | io |
| Igbo | ig |
| Indonesian | id, in |
| Interlingua | ia |
| Interlingue | ie |
| Inuktitut | iu |
| Inupiak | ik |
| Irish | ga |
| Italian | it |
| Japanese | ja |
| Javanese | jv |
| Kalaallisut, Greenlandic | kl |
| Kannada | kn |
| Kanuri | kr |
| Kashmiri | ks |
| Kazakh | kk |
| Khmer | km |
| Kikuyu | ki |
| Kinyarwanda (Rwanda) | rw |
| Kirundi | rn |
| Kyrgyz | ky |
| Komi | kv |
| Kongo | kg |
| Korean | ko |
| Kurdish | ku |
| Kwanyama | kj |
| Lao | lo |
| Latin | la |
| Latvian (Lettish) | lv |
| Limburgish ( Limburger) | li |
| Lingala | ln |
| Lithuanian | lt |
| Luga-Katanga | lu |
| Luganda, Ganda | lg |
| Luxembourgish | lb |
| Manx | gv |
| Macedonian | mk |
| Malagasy | mg |
| Malay | ms |
| Malayalam | ml |
| Maltese | mt |
| Maori | mi |
| Marathi | mr |
| Marshallese | mh |
| Moldavian | mo |
| Mongolian | mn |
| Nauru | na |
| Navajo | nv |
| Ndonga | ng |
| Northern Ndebele | nd |
| Nepali | ne |
| Norwegian | no |
| Norwegian bokmål | nb |
| Norwegian nynorsk | nn |
| Nuosu | ii |
| Occitan | oc |
| Ojibwe | oj |
| Old Church Slavonic, Old Bulgarian | cu |
| Oriya | or |
| Oromo (Afaan Oromo) | om |
| Ossetian | os |
| Pāli | pi |
| Pashto, Pushto | ps |
| Persian (Farsi) | fa |
| Polish | pl |
| Portuguese | pt |
| Punjabi (Eastern) | pa |
| Quechua | qu |
| Romansh | rm |
| Romanian | ro |
| Russian | ru |
| Sami | se |
| Samoan | sm |
| Sango | sg |
| Sanskrit | sa |
| Serbian | sr |
| Serbo-Croatian | sh |
| Sesotho | st |
| Setswana | tn |
| Shona | sn |
| Sichuan Yi | ii |
| Sindhi | sd |
| Sinhalese | si |
| Siswati | ss |
| Slovak | sk |
| Slovenian | sl |
| Somali | so |
| Southern Ndebele | nr |
| Spanish | es |
| Sundanese | su |
| Swahili (Kiswahili) | sw |
| Swati | ss |
| Swedish | sv |
| Tagalog | tl |
| Tahitian | ty |
| Tajik | tg |
| Tamil | ta |
| Tatar | tt |
| Telugu | te |
| Thai | th |
| Tibetan | bo |
| Tigrinya | ti |
| Tonga | to |
| Tsonga | ts |
| Turkish | tr |
| Turkmen | tk |
| Twi | tw |
| Uyghur | ug |
| Ukrainian | uk |
| Urdu | ur |
| Uzbek | uz |
| Venda | ve |
| Vietnamese | vi |
| Volapük | vo |
| Wallon | wa |
| Welsh | cy |
| Wolof | wo |
| Western Frisian | fy |
| Xhosa | xh |
| Yiddish | yi, ji |
| Yoruba | yo |
| Zhuang, Chuang | za |
| Zulu | zu |
