Answer on Can someone tell me more about indigenous Greek and Albanian speaking populations of southern Italy?
The Arbereshe are Albanian-descended peoples who live in Albanian communities usually in southerly parts of Italy (from Abruzzo region and south down to Sicily basically). They generally are Catholics, but generally Byzantine (Eastern Rite) Catholics rather than Roman (Latin) Catholic. Some of their communities have been there hundreds of years (originally left Albania fleeing the Ottoman Turks in many cases). Most Albanians in Albania are either Muslim or Eastern Orthodox today, with a small (usually Eastern) Catholic minority. They call themselves Shqiptare as opposed to the Albanians in Italy who are called Arbereshe. The Arberehse generally don't mix much with the local non-Albo population (tend to date and marry at least within their own kind). You can look up Piano degli Albanese in Sicily for one large Arbereshe community.
All I know about the Griko speakers was that they are from Calabria usually (I think around Reggio di Calabria area), and they are distinct minority community. Very small numbers who actually speak this language, which I think is not proper Greek but really more like a dialect of it. They used to be in small villages away from the world, in isolated mountainous regions in Calabria, but most have left those villages and today most of their children speak regular Italian (or local Italian dialect). It's almost a dead language, I would say, well not quite dead but a very tiny number of Griko speakers remaining today in Calabria (probably older people in remote villages and such).