HTML 的 lang 属性可用于声明网页或部分网页的语言。这对搜索引擎和浏览器是有帮助的。
根据 W3C 推荐标准，您应该通过 <html> 标签中的 lang 属性对每张页面中的主要语言进行声明，比如：
在 XHTML 中，采用如下方式在 <html> 标签中对语言进行声明：
ISO 639-1 为各种语言定义了缩略词。您可以在 HTML 和 XHTML 中的 lang 和 xml:lang 属性中使用它们。
| 语言 | ISO 代码 |
|---|---|
| Abkhazian | ab |
| Afar | aa |
| Afrikaans | af |
| Albanian | sq |
| Amharic | am |
| Arabic | ar |
| Aragonese | an |
| Armenian | hy |
| Assamese | as |
| Aymara | ay |
| Azerbaijani | az |
| Bashkir | ba |
| Basque | eu |
| Bengali (Bangla) | bn |
| Bhutani | dz |
| Bihari | bh |
| Bislama | bi |
| Breton | br |
| Bulgarian | bg |
| Burmese | my |
| Byelorussian (Belarusian) | be |
| Cambodian | km |
| Catalan | ca |
| Cherokee | |
| Chewa | |
| Chinese (简体) | zh |
| Chinese (繁体) | zh |
| Corsican | co |
| Croatian | hr |
| Czech | cs |
| Danish | da |
| Divehi | |
| Dutch | nl |
| Edo | |
| English | en |
| Esperanto | eo |
| Estonian | et |
| Faeroese | fo |
| Farsi | fa |
| Fiji | fj |
| Finnish | fi |
| Flemish | |
| French | fr |
| Frisian | fy |
| Fulfulde | |
| 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 |
| Hawaiian | |
| Hebrew | he, iw |
| Hindi | hi |
| Hungarian | hu |
| Ibibio | |
| Icelandic | is |
| Ido | io |
| Igbo | |
| Indonesian | id, in |
| Interlingua | ia |
| Interlingue | ie |
| Inuktitut | iu |
| Inupiak | ik |
| Irish | ga |
| Italian | it |
| Japanese | ja |
| Javanese | jv |
| Kannada | kn |
| Kanuri | |
| Kashmiri | ks |
| Kazakh | kk |
| Kinyarwanda (Ruanda) | rw |
| Kirghiz | ky |
| Kirundi (Rundi) | rn |
| Konkani | |
| Korean | ko |
| Kurdish | ku |
| Laothian | lo |
| Latin | la |
| Latvian (Lettish) | lv |
| Limburgish ( Limburger) | li |
| Lingala | ln |
| Lithuanian | lt |
| Macedonian | mk |
| Malagasy | mg |
| Malay | ms |
| Malayalam | ml |
| Maltese | mt |
| Maori | mi |
| Marathi | mr |
| Moldavian | mo |
| Mongolian | mn |
| Nauru | na |
| Nepali | ne |
| Norwegian | no |
| Occitan | oc |
| Oriya | or |
| Oromo (Afaan Oromo) | om |
| Papiamentu | |
| Pashto (Pushto) | ps |
| Polish | pl |
| Portuguese | pt |
| Punjabi | pa |
| Quechua | qu |
| Rhaeto-Romance | rm |
| Romanian | ro |
| Russian | ru |
| Sami (Lappish) | |
| Samoan | sm |
| Sangro | 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 |
| Spanish | es |
| Sundanese | su |
| Swahili (Kiswahili) | sw |
| Swedish | sv |
| Syriac | |
| Tagalog | tl |
| Tajik | tg |
| Tamazight | |
| Tamil | ta |
| Tatar | tt |
| Telugu | te |
| Thai | th |
| Tibetan | bo |
| Tigrinya | ti |
| Tonga | to |
| Tsonga | ts |
| Turkish | tr |
| Turkmen | tk |
| Twi | tw |
| Uighur | ug |
| Ukrainian | uk |
| Urdu | ur |
| Uzbek | uz |
| Venda | |
| Vietnamese | vi |
| Volapük | vo |
| Wallon | wa |
| Welsh | cy |
| Wolof | wo |
| Xhosa | xh |
| Yi | |
| Yiddish | yi, ji |
| Yoruba | yo |
| Zulu | zu |