There are around 5000 people today in the province of Chubut, Patagonia in southern Argentina, who speak Welsh, the descendants of 150 Welsh emigrants who left Wales to settle in Patagonia in 1865. In a piece on the BBC website Professor E Wyn Jones from Cardiff University talks about a recent visit he made to the area, and noted that he felt he was in a parallel universe, where people sing Welsh hymns and do Welsh folk dancing.
The remote region of Patagonia was hit upon by these 19th-century Welsh patriots so that they could maintain their language and culture. Yet today they are proudly Argentinian, although also proud of their Welsh background. At the beginning of the 20th century the 'Welshness' of the region was suppressed by the Argentine government but today there are ever more links between the region and Wales, and a growing revival of interest in Welsh language and culture. Welsh is still in use (albeit by a minority - as in Wales itself), there are people learning Welsh, nonconformist chapels and eisteddfodau. As Jones says, here Welsh is spoken with a Spanish lilt.
Here's the interesting BBC article.