Azizi - you were asking about the relationships of different celtic languages.

Briefly Celtic languages are a branch of Indo-european and descended from proto-celtic. There are 4 sub families:

Gaulish and its close relatives, Lepontic and Galatian. These languages were once spoken in a wide arc from France to Turkey and from Belgium to northern Italy.

Celtiberian, anciently spoken in the Iberian peninsula, namely in the areas of modern Portugal, Galicia, Asturias, Cantabria, Aragón and León. (I think some of these languages may still be spoken locally, but I'm not sure)

Goidelic, including Irish, Scots Gaelic, and Manx.

Brythonic (also called Brittonic), including Welsh, Breton, Cornish, Cumbric, the hypothetical Ivernic, and Pictish.

TThe last 2 groupings are the ones currently and previously spoken in Britain and Ireland and are often also called Q Celtic and P celtic respectively, but I'm not sure how the other 2 groupings fitted into that classification.

Irish and Irish Gaelic are interchangeable terms - when writing about Gaelic you have to qualify whether you are talking about Scots or Irish Gaelic. Although spelt the same, and pretty closely related, the two are pronounced differently. Irish gaelic is Gay-lick and scots gaelic is Gah-Lick.

Find out more at http://en.wikipedia.org/wiki/Celtic_languages

Bagpuss