This can be misleading for speakers of other Romance languages.
At least in case of Romanian, "verde" means "green", same as in Italian and Spanish, however the only word derived from it used for food (verdeturi) refers only to all types of green leafs we put in our food (from dill an parsley to all types of salads). For all veg we use "legume" (from Lat. legumen), which was kept also in French Portuguese, but surprisingly not in Italian... Or is it still used in some of its dialects?
Hi Manly, "vegetable", as "verdura", is a collective noun,in Italian the singular has a general meaning ( usually more associated to the edible one),vegetables in their entirety, with the plural we think to them as single components. In English vegetable is also an adjective , in Italian "vegetale"
For sure you can say only "mangia" without a third person singular pronoun, however in cases of misunderstanding or clarification, it's better if you put the right pronoun before the verb. For example, if the gender of the one who is doing the action in the sentence is important, you should write the pronoun to avoid confusion.
Mangia. - He/She/It eats. > When you are sure the receiver will understand about whom you are talking.
Lei mangia. - She eats. > When, for example, a girl in a group of boys eats something.
I would say that your examples would fall under the category of slang. It's informal and very regional. It's the sort of thing that someone from elsewhere might not intuitively understand. You can often tell where someone is from by the slang they use. Here in the US, a carbonated beverage is called a, "Coke," "soda," or "pop" depending on where one was raised. I wouldn't expect any general language curriculum to except slang, like "ain't."