属性lang是英语language的缩写，意思是语言。如：”en”代表英语，”zh-CN”代表中文。详细描述请看下面的表格。
在页面布局方面，其实不写lang属性，整个HTML文档的显示是没有任何问题。
 
但是，lang会帮助浏览器（如谷歌浏览器）提示是否需要翻译网站。
 
另外一点，搜索引擎首先自己无法判断自己抓取的页面中的内容是什么语言，因为在它看来都是二进制文件，我们需要告诉它这个页面中的内容是什么语言，进而它才能知道下一步该干嘛。进而能更好地帮助搜索引擎整理索引内容。
 

ISO 639-1标准lang属性代码参考
Language ISO Code
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 (简体中文) zh-Hans
Chinese (繁体中文) 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