The Celtic languages are a subgroup of the Indo-European language family. The language family is divided into two groups: The Continental Celtic languages (all of which are now extinct) and the Insular Celtic Languages.
Continental Celtic languages
Continental Celtic languages were once widespread throughout Europe with a range from northern Portugal in the west to central Anatolia in the east. However today all Continental Celtic languages are extinct, largely replaced by Germanic and Italic languages in West and Central Europe, Slavonic languages in the Balkans and Turkish in Anatolia. Not enough is known about many of the continental Celtic languages to precisely determine their relationships with each other.
Celtiberian was spoken in northern Spain and shares some features with Insular Goidelic languages.
Gaulish was spoken in France as well parts of Belgium, Switzerland and northern Italy.
Lepontic was spoken in parts of Austria and northern Italy.
Noric was spoken in parts of Austria and Slovenia.
Galatian was spoken in the area around Ankara in Anatolia.
Lusitanian (Extinct) (uncertain affiliation)
Lusitanian was a language spoken in northern Portugal, it is uncertain whether it was truly a Celtic language at all.
Insular Celtic languages
The Insular Celtic languages originated in the British Isles and are further divided into Goidelic and Brythonic groups.
Gàidhlig was once the main language of Scotland and some far northern extremes of England although it never totally dominated the whole of Scotland. Today it is mainly limited to the north and west of the country. The main bastions of Gàidhlig are the western isles.
Gaeilge was at its height the dominant language throughout Ireland and parts of western Wales, since the 12th century it has been in decline and is now only truly spoken as a community language in relatively isolated parts of western Ireland.
Gaelg is the Manx variety of Gaelic, it is closer to Gàidhlig than Gaeilge but has a distinct spelling system and a high proportion of Norse loanwords. The last native speaker died in 1974, but the language is currently undergoing a resurrection.
Cumbric is the extinct brythonic language of northern England and southern Scotland. The language was closely related to Welsh. In the south the language gradually gave way to Anglic and in the north to Gàidhlig. It is estimated that Cumbric went extinct some time around the 12th century.
Cymraeg is the official language of Wales, it is widely spoken in north Wales, particularly amongst the older and younger generations reflecting the fact that it is a language in revival. Cymraeg is also spoken in some areas in the Argentinian region of Patagonia. Of all Celtic languages Cymraeg has the largest number of first language speakers.
Brezhoneg is spoken in Brittany, particularly the western regions. Although Brezhoneg is spoken by people on the European continent it is not a Continental Celtic language as was once thought, but is actually an insular Celtic language closely related to Kernewek. Brezhoneg faces problems with ageing speakers and resistance to Brezhoneg education by the French central government.
Kernewek was once the language of Cornwall, Devon, Somerset and Dorset. Anglo-Saxon conquests pushed the language further and further west until Kernewek was spoken only west of the river Tamar. Later the English language continued the encroachment of Kernewek from the east until according to Richard Carew's Survey of Cornwall in 1602 the language was almost totally gone. Today there are no native speakers, but a few people are fluent speakers of Kernewek as a second language and interest in the language is increasing.
Pictish is a little understood language that was spoken in East Scotland before being replaced by Gàidhlig, no consensus has been reached on exactly where it fits within the Celtic language group. Some linguists hold that Pictish is closely related to Gaulish whilst others claim it is a Brythonic language closely related to Welsh. A likely explanation is that Pictish was most closely related to the Brythonic languages but had diverged from them early and still contained a higher influence from Continental Celtic languages.