Silent S in isla?
I heard it on the Canary islands news. They pronounce Z and C like in Latin America but the S in "isla" and last "s" like in plurals is often dropped by some locals (but not by the TV presenters). The TV hosts DO say the z and c like local islanders and American Hispanics do. I thought only final -s was silent in the Canary Islands, but even in isla? I hear "ilya", similar to PT "ilha". Is it considered undesirable slang? A Portuguese influence?
No, it is not dropped. It is aspirated. They don't say "ila", they say "isla" with aspirated s (ihla). Listen to "cascos" in Forvo https://forvo.com/word/cascos/#es , the second pronunciations is with aspirated s. If you hear "caco", my answer is right. If you hear something different to "caco", maybe you met some islanders who actually drop s's, but it is unlikely.
Thanks. So islanders and some Latin Americans e.g. from Chile aspirate it, but Mexicans and mainland Spain do not, right? There are loads of -s pronounced strongly in Mexican telenovelas.
You are welcome. Aspiration is normal in Andalusian, Canarian, Caribbean (it includes Venezuela and Caribbean coast of Mexico and Colombia), Chilean, Rioplatense, Paraguayan, Eastern Bolivian ("Camba") and coastal varieties from Peru and Ecuador. If you mark this distribution in a map of the Americas you'll see why they are called "hablas de las tierras bajas americanas".
alezzzix is right, gemination is also possible. It is common in Andalusian, not only for s, but also for final r's: "Etta canne ettá bien cottá".
I think it might be a case of gemination, basically the 's' at the end of a syllable can produce the lengthening of the next consonant in certain speakers, which would explain why you're hearing something similar to the Portuguese ilha. If that's the case, then isla would be pronounced with a double ll (I mean literally, not the 'y' sound), just like the word poste would be pronounced 'potte' (longer 't' sound). It's probably something that you would rather avoid doing in formal situations.