A side note: as a teenager I spent one summer working in a clothing store in London, with a bunch of Spaniards and Italians. They spoke to each other using their respective tongue, and said they could understand each other. Just basics of course.
Maybe someone from Spain or Italy could chime in here?
As with the Arabic and Chinese language families, different varieties of Romance languages are similar enough in syntax and vocabulary that speakers can kind of make themselves understood to each other if they speak slowly and choose their words carefully. Same with lots of closely related languages, e.g. German and Dutch. But they're not nearly mutually intelligible to the degree that American English and most varieties of British English are or that Hindi and Urdu are.
Regarding the Spanish/Italian example, the father of a friend of mine was fluent in Spanish, French, and Portuguese. Using an Italian grammar guide and his knowledge of Romance vocabulary from the other three languages, he learned Italian in a single flight from the US to Italy to the point where he was able to conduct business in Italy immediately upon landing.
I'm Dutch, and people from the east of Netherland don't understand why I don't understand German, claiming the languages are so similar. But I have real trouble understanding German. Maybe when it's someone from the north-west of Germany who speaks very slowly and clearly. People from the east of Netherland have much less trouble, somehow.
(I'm utterly unable to understand people from the Dutch province of Zeeland when they're speaking to their parents. That's complete gibberish to me, though it doesn't have a special status as a local language, as far as I know. (unlike Nethersaxon, for example))
When you have trouble understanding germans, are they speaking Hochdeutsch or Platt? I'm curious if Platt is more closely related to Dutch than Hochdeutsch or not.
As a german, I always have problems understanding other germans when they speak english, so there's always that ;).
I'm Romanian, as a kid in a few months I became fluent in Italian just from watching their TV channels, no dictionary involved. It was a mass phenomenon at the time since their TV channels were quite popular on cable.
As a French I can tell you we can understand most of casual Italian / Spanish conversation just fine (and I believe Spaniards and Italians can understand a good portion of French too). The roots are very similar for most words that you catch it up very quickly.
In "The Grammar of Romanian"[1] book, Romanian language contains the following: 20 percent inherited Latin, 11.5 percent Slavic, 3.6 percent Turkish, 2.17 percent Hungarian, 43 percent Romance borrowings (mainly French - 38.4 percent).
The lexical similarity of Romanian with Italian has been estimated at 77%, followed by French at 75%, Sardinian 83%, Catalan 73%, Portuguese and Rhaeto-Romance 72%, Spanish 71%.
In modern times Romanian vocabulary has been strongly influenced by French, Italian and other languages.
Phonemes are similar, but spoken Romanian is complete gibberish to me.
Things get better in writing, but there's still no comparison to Spanish.
After all there was a longer interaction with the latter: for historical reasons words and verbal constructs in southern dialects can give insights with regard to it or French.
As a portuguese who learnt some french in school, portuguese, spanish and italian are all similar enough that you can communicate or at least kind of understand what's being talked about. Spanish is the closest to portuguese though (how entirely unsurprising), and the degree to which I understand italian is quite influenced by knowing some french.
As a person currently studying Spanish, I can understand basic Portuguese, Italian, French.
As all these languages are from the same origin (Latin).
Similarly, although Hindi is derived from Sanskrit, over the years, due to lots of Mughal invasions, and Urdu arts, poets, a lot of Urdu words are a part of Hindi. Hence they are easily understood in either part of the border.
As a Spaniard that has visited Italy, I can attest that they definitely understand us and we understand them, at least for the basics. However, there are interesting differences, like the way we pluralize words (quite different in both languages) or the lack of certain prefixes that Spanish imported during the Arabic occupation (carciofo -> alcachofa, zucchero -> azúcar, etc). I haven't studied Italian but I guess that the grammar is very similar.
It's a little like Galician or Catalonian (languages without an army or navy ;) ), the other latin languages spoken in Spain (then there is Basque, but that's a completely different thing): they have palpable differences to Spanish, but in most cases both tongues can reasonably understand each other without many problems (it also helps that most Galician and Catalonian speakers also speak Spanish, of course).
Maybe someone from Spain or Italy could chime in here?