Languages of Sardinia
Modern linguistics tends to avoid the term "dialect" because of the negative connotations connected with that word (as in "Oh, that's just a dialect.") It is much easier —and linguistically precise— to call everything a "variety of language" or, better, simply a "language." ("Languages" may be official; "dialects" are not; that is, as linguists like to joke, a language is a dialect with an army (!) —or at least the political power to declare itself "official." As Latin splintered along with the Roman Empire, the pieces —dialects— became "real" languages when the people who spoke a particular regional brand of vernacular medieval Latin got enough clout to declare that theirs was the official language of the area they lived in; the reason we have Spanish, Portuguese, Italian, and French is that we first had Spain, Portugal, Italy and France. Now we have Catalan, Gallician, and Sardinian. All of those languages are members of the Romance family of languages, a branch of the larger Western Indo-European family. Isolation tends to discourage rapid language change, and Sardinia is obviously isolated; thus, the languages spoken on the island are relatively conservative; that is, they have changed, but slowly, over the centuries.
When we say that Sardinian is a Romance language and, thus, related to Spanish, French, and Italian, we are saying that just as in Spain, France, and Italy, Roman domination had a lot to do with the language(s) spoken on the island. Indeed, Rome ruled Sardinia from the date of the first Punic War (238 BC) until the fall of the Roman Empire (the late 400s). Thus, anyone who reads Spanish or Italian can look at the written Sardinian language and see that it is a "Latin" language. Yet, the island had a long history before the Romans arrived, a history of many peoples speaking their languages. We know that the Phoenicians settled on Sardinia; before that we know that an early Sardinian culture built the many nuraghi; and before that, there were the peoples of the Ozieri culture, the late Neolithic and Copper Age communities in the north of Sardinia. We should thus expect to find in Sardinian languages some influences of pre-Latin languages that exist at the level of what linguists call the substrate—deep down below the Latin, just as we find examples of ancient Greek in languages on the southern Italian peninsula. One also expects to find later influences from Byzantine Greek and Spanish on Sardinia. (If you find some Basque or Etruscan, good for you! —you are learning just how complicated this can be.) For our purposes, it is enough to note that, indeed, the languages of modern Sardinian are Romance, but that they are built on a very rich substrate of other earlier influences. Thus, in many Sardinian languages we have from Phoenician the word míntza for water or spring; cúcuru (summit or mountain top), especially interesting since there is a Basque word, kukur, that means the same thing (thus there may be a proto-Iberian influence). There are pre-Latin grammatical influences, as well, having to do, for example, with the way words form plurals or the uses of prefixes and suffixes, etc.
Linguists look at all this and tell us that, roughly, you can divide "Sardinian" into northern, central, and southern varieties; additionally, there are interesting sidelights such as the existence in the northwest of a Catalan variety of Sardinian (that is, people from Alghero on the northwest coast of Sardinia can easily converse with people in Barcelona in Spain) and the similarity between extreme northern Sardinian and the language spoken at the southern tip of Corsica, the island just a few miles away to the north. From extreme south to extreme north, the regional varieties of language are not necessarily mutually comprehensible any more than Spanish and Italian are.
We are in the midst of a Europe-wide recognition of minority languages; thus, we now have four official languages in Spain, and, in the "semi-autonomous" Italian region of Sardinia, there is now recognition of the "Sardinian language." It is difficult, however, to gauge exactly what this means. At the very least, it means that a Limba Sarda Comuna (Common Sardinian Language), a compromise language of regional varieties worked out by scholars, now exists and its use is encouraged. Although standard Italian is obviously the major language of the island, it is common to see, for example, signs in Sardinian and find instructional media in Sardinian for schools, and to find television and radio programs in the language. Official documents may also appear in Sardinian (and Italian); that is a step further than is the case with other "dialects" in most other parts of Italy. (There is, for example, no official use of "Neapolitan" in the Campania region of Italy.) This has to do with the "semi-autonomous" status of Sardinia.