I'm from Milan, Italy. (Sorry for my English)
As for your first question...The girl speaking in this file, speaks a Standard Italian with a Northern accent. She isn't speaking in dialect.
She says that she is very happy because she is planning to marry.
Her accent is surely from northern regions, maybe near Swiss.
2. I think, Italian dialects are not mutually intelligible...I mean..that for me that I live in Milan is easier to understand an English man...than a man who speaks in for example the dialect of naples or palermo!
Dialects are very difficult to understand. I think a person from Bergamo cannot understand one from Naple.
Italy unified only in 1861 so...there were many different realities, influences, traditions, castles, exc...
today the majority of northern people, speaks a standard italian sometime with a soft accent. The north is very multicultural and international, today.Maybe in the small countries and old people, use dialect to speak. But everywhere you find standard italian.
In the centre and in the south, you will find, much more tradition and people who speak in dialect in its everyday language, but also know the italian because studied it at school. When they speak standard italian, they have an heavy accent and often is not easy to understand them. They have also different terms for things and way of speaking.
What I assure you, is that an italian can't understand another italian who speak in dialect.
There are differences even in cities very near!
In my family only grandma knows dialect. She is from cremona (Milano), every small town has its own dialect.Grandma is 95 years old...and know speaks a perfect standard italian.
I can't understand her if she speaks in cremonese...many words are similar to french or austria...because also for the domination in the past centuries...
televisions programms and papers are in standard italian (except some comic actor)
3. Italian speakers...don't really understand...spanish, portoguese or french...but understand...some words...Our languages are very similar...because come from Latin(romans).
so we have many words in common.
Last december I went to france. I don't speak french...but if they spoke slowly I understood the meaning of the phrase...and they...the same...If I spoke in italian...slowly, they understood!Someone told me to speak in italian, and not english...because they could understand better.
spanish is very very similar.
for example: amore (love) - spanish amour!
pantaloni (trousers, jeans,) - french pantalon !
infante (child) - french enfants
patria (homeland) - french patrie
buongiorno (good morning) french bon jour
food is very similar...cheeses and wines.