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Internationally, for the purposes of the European Charter for Regional or Minority Languages, "regional or minority languages" means languages that are:
- traditionally used within a given territory of a State by nationals of that State who form a group numerically smaller than the rest of the State's population; and
- different from the official language(s) of that State
Influence of number of speakers 
There are many cases when a regional language can claim greater numbers of speakers than certain languages which happen to be official languages of sovereign states. For example, Catalan (a regional language of Spain, Italy and France, albeit the national language of Andorra) has more speakers than Finnish or Danish. In China, Wu, spoken in southern Jiangsu, northern, and the general area of Shanghai Zhejiang by more than 90 million speakers, can claim more native speakers than French, and Cantonese, a regional language of Guangdong, Hong Kong and nearby areas in China with more than 60 million local and overseas speakers (North America, parts of Malaysia), outnumbers Italian in number of speakers. Subgroups and dialects of the Min group have over 70 million speakers, mainly in Fujian and in nearby Taiwan, but also in the Southeast Asian countries of Malaysia and Singapore.
Relationship with official languages 
In some cases, a regional language may be closely related to the state's main language or official language. For example:
- The Frisian languages, regional languages of the Netherlands and Germany, belong to the Germanic family.
- The Gutnish language, a regional language spoken in Gotland and related to the Swedish language.
- Westrobothnian is another Swedish regional language native to historical Westrobothnia.
- Regional languages of Han Chinese, belong to the same family of Chinese languages as Mandarin. Some regional languages of minority groups such as Amdo Tibetan language have regional official status.
- Kashubian, a regional language of Poland.
- Limburgish, a regional language in Germany, the Netherlands and Belgium, has around one million speakers and is closely related to Luxembourgish, Rhinelandic and Ripuarian.
- Low German (also referred to as Low Saxon), an officially recognized regional language in Germany and the Netherlands, the direct descendant of Old Saxon. Sometimes (e.g. by nds and nds-nl Wikipedia) considered two languages divided by today’s Netherlands–German border on account of Dutch influences in the west and German influences in the east; closely related to Frisian, more distantly to German.
- Scots, a regional language of Scotland and Ireland, belongs to the same family of West Germanic languages as English.
- Regional languages of Spain and Portugal:
- Aranese, Catalan, and Galician are each, in the regions where they are the autochthonous language, co-official in status with Castilian (Spanish) which is official everywhere in the Kingdom of Spain.
- Asturian and Leonese are recognized (but unofficial) in Asturias and Castile and León (Spain), while Mirandese is co-official with Portuguese in Miranda do Douro (Portugal). These Romance languages are classified under the term Astur-Leonese languages. Astur-Leonese is closely related to both Castilian and Galician, which itself is most closely related to Portuguese. Catalan is an Occitano-Romance language.
- Occitan, most widely spoken across the Pyrenees in France and Catalonia, together with Catalan, forms a subgroup of Romance languages linguistically intermediate between French and the Ibero-Romance languages of Spain and Portugal. Aranese is a subdialect of Gascon
- Võro, a regional language of Estonia, belongs to the same family of Finnic languages as Estonian.
- Walloon, a regional language of France and Belgium, belongs to the same family of Oïl languages as French.
In other cases, a regional language may be very different from the state's main language or official language. For example:
- Basque, a regional language in Spain and France, is a language isolate.
- Breton is a regional Celtic language spoken in Brittany, part of France.
- Cornish, is a non-living regional Celtic language originating in Cornwall, England.
- Corsican, a regional language in France (Corsica) closely related to Tuscan.
- Gagauz, a regional Turkic language used in Moldova.
- Livonian, a regional language of the Finnic family spoken in Latvia.
- Neapolitan, is the regional language of Naples and the southern continental Italy, also known as Southern Italian and Neapolitan–Calabrian.
- Resian, a dialect of Slovene, is a regional language spoken in eastern Italy.
- Sardinian, a regional language in Italy (Sardinia) which is considered to be the most conservative of the Romance languages in terms of archaic phonetic and morphosyntactic phenomena.
- Scottish Gaelic is a regional Celtic language spoken in the highlands of Scotland, part of the United Kingdom.
- Sorbian, a regional language of Germany, is a Slavic language.
- Welsh is a regional Celtic language spoken in Wales, part of the United Kingdom. In November 2010 the Welsh Assembly passed a Measure that made Welsh and English the official languages of Wales.
Official languages as regional languages 
An official language of a country may also be spoken as a regional language in a region of a neighbouring country. For example:
- Afrikaans, an official language of South Africa, is a regional language of Namibia.
- Cantonese, one of the official languages in Hong Kong and Macau (both special administrative regions of the People's Republic of China), is used as a regional language of the province of Guangdong, People's Republic of China.
- Catalan, the official language of Andorra, is a regional language in Spain (Catalonia, Balearic Islands and Valencian Community), France (Pyrénées Orientales) and Italy (Alghero).
- German, an official language of Austria, Belgium, Germany, Liechtenstein, Luxembourg and Switzerland, is a regional language in Italy (South Tyrol), Poland (Silesia), France (Alsace and Lorraine) and Denmark.
- Hungarian, a Uralic language and official in Hungary, is a regional language of Romania whose official language, Romanian is a Romance language.
- Irish, the first official language of the Republic of Ireland, is a regional language in Northern Ireland which is a constituent country of the UK.
- Korean, the official language of Korea, is a regional language in People's Republic of China (Yanbian Korean Autonomous Prefecture).
- Russian, the official language of the Russian Federation and Belarus, is a regional language of Abkhazia, South Ossetia and other entities.
- Turkish, the official language of Turkey and Cyprus, is a regional language of Kosovo.
See also 
- Minority language
- National language
- Languages of France
- Languages of the European Union
- British-Irish Council
- Languages in the United Kingdom
- List of languages of Italy