Scottish Gaelic is spoken by about 58,000 people in Scotland (Alba), mainly in the Highlands (a' Ghaidhealtachd) and in the Western Isles (Na h-Eileanan an Iar), but also in Glasgow (Glaschu), Edinburgh (Dùn Eideann) and Inverness (Inbhir Nis). There are also small Gaelic-speaking communities in Canada, particularly in Nova Scotia (Alba Nuadh) and on Cape Breton Island (Eilean Cheap Breatainn). Other speakers can be found in Australia (Astràilia), New Zealand (Sealainn Nuadh) and the USA (Na Stàitean Aonaichte).
Relationship to other languages: Scottish Gaelic is closely related to Manx and Irish and was brought to Scotland around the 4th century AD by the Scots from Ireland. Scottish Gaelic was spoken throughout Scotland (apart from small areas in the extreme south-east and north-east) between the 9th and 11th centuries, but began to retreat north and westwards from the 11th century onwards. All Scottish Gaelic dialects are mutually intelligible, and written Irish can be understood to a large extent.
Scottish Gaelic is also distantly related to Welsh (Cymraeg), Cornish (Kernewek) and Breton (Brezhoneg), which form the Brythonic branch of the Celtic languages, also known as P-Celtic. The Celtic languages all have a similar grammatical structure, but have relatively little vocabulary in common.
source
wikipedia.org,
omniglot.com,
evertype.com &
ethnologue.com