af: Inligting oor landkodes, taalkodes en Wikipedia.
de: Informationen zu Landeskenncodes, Sprachenkenncodes und Wikipedia.
en: About country codes, language codes, and Wikipedia.
el: Σχετικά με κώδικες χωρών, γλωσσικούς κώδικες και Wikipedia.
es: Sobre códigos de país, códigos de la lengua, y Wikipedia.
fi: Tietoa maa- ja kielikoodeista sekä Wikipediasta.
fr: Au sujet des codes de pays, des codes de langue et de Wikipedia.
gl: Sobre códigos de países, códigos de linguas e Wikipedia.
it: Circa i codici di paese, i codici di lingua e Wikipedia.
jp: 国番号、言語コード、およびWikipedia について。
ko: 국가 번호, 언어 부호, 및Wikipedia에 관하여.
lt: Apie valstybių, kalbų kodus ir Wikipediją
nl: Over landcodes, taalcodes en Wikipedia.
pt: Sobre códigos da língua, e Wikipedia.
ru: О кодах стран, кодах языков и Википедии.
The International Organization for Standardization (ISO), located in Geneva, Switzerland, maintains the official lists of standard 2-letter (or 3-digit) country/territory/region codes as part of the ISO 3166-1 standard. More information is at http://www.iso.ch/
These ISO 3166-1 codes are also (partly) reused for internet addresses as country-code top-level domains, but they are historically assigned by IANA (now based on ISO 3166-1 but with some historical differences) and may remain valid as top-level domains even if their use as country/territory/region codes as been retired by ISO.
ISO also assigns separately 2-letter or 3-letter codes for languages or groups of language as part of the ISO 639 standard, within several sets with distinct use cases (bibliographic or semantic).
These codes are also reused (partly) on the Internet as part of the BCP 47 (and registered in a IANA database for language subtags). For some languages (or group of languages), there may be multiple codes defined (possibly with different scopes for historical 2-letter codes from ISO 639-1 or ISO 639-2). Some of these codes may become removed by ISO (after further research and classification), but codes that were added into the IANA database for BCP 47 language subtags will remain valid, even if they are marked as deprecated with one or several preferred codes listed. As well some language variants (such as "simple" for Simple English) may have standard codes registered as BCP 47 language subtags, that do not match any ISO 639 code.
Even if the list of codes for languages or for country/territories/regions defined by ISO have become the most widely used, there still exists several competing standards in some national or international standard bodies or organizations (such as "EL" for Greece, used by the European Union and matching the ISO 639 code "el" for the Greek language and not "GR" for Greece; or codes used for identifying vehicles on car plates, or codes defined by the Universal Postal Union, codes used in various protocols defined by the International Telecommunication Union, and other codes defined byb national standard bodies of some countries for their own national standards).
Sometimes a country code is the same as the language code of the language most often spoken there, other times the same letter sequence is used for unrelated languages and countries (e.g. "uk" for Ukrainian, but "UK" for the United Kingdom); frequently as well, the language code and country code won't match (e.g. "ja" for Japanese, but "JP" for Japan; "uk" for Ukrainian, but "UA" for Ukraine).
Some Wikipedias are also registered with country-code top-level domains (ccTLD). If the country generally uses one language, it redirects automatically to that linguistic edition of Wikipedia. For example, "http://www.wikipedia.de/" redirects to "http://de.wikipedia.org/". If the country uses multiple languages, the page serves as a portal to each language used in that country. Some countries also have several codes registered or reserved (as well its ccTLD like ".uk" may not not the standard ISO country code "GB" which is still reserved as ".uk" as an unused ccTLD, but there are additional codes for dependant territories of Australia, Denmark, France, Finland, the People's Republic of China, the Netherlands, New Zealand, the United Kingdom, or the United States).
Note that when they are used in domain names, nothing requires any wiki to use valid country codes or language codes. They are only limited by rules applicable to the DNS and the relevant domain name registries (for top-level domains) and those defined privately in each subdomain name. Wikipedia for example can still use some codes that do not match the expected language code, or may define codes for specific uses or variants for assigning a domain name to its wikis, or (separately) for its "interwiki codes". Some of these legacy codes may become aliases to standard codes, but the reverse is also possible and will not be fixed before long.