I'm out of practice, but I believe it's an irregular plural - much like "goose/geese" or "mouse/mice" in English. Some words, particularly well-used ones, will not follow the pattern that most words follow. This should be better explained on the tool tip at the introduction of this word.
It is perfectly okay to ask why and every seemingly illogical and irregular feature in languages has a logical reason and interesting history behind it, and it opens up a whole new world of knowledge to one if one just bothers to explore more. Back to the topic: Italian word uomo derives from Latin word homō, which also means man, mankind. Homō is a third declension word and it is in nominative case, its root is homin-, and its nominative plural is hominēs, which developed into Italian plural for uomo, uomini. I recommend Wiktionary, it can sometimes provide quite detailed etymological information. http://en.wiktionary.org/wiki/uomini
That may be, but I think what they are trying to say is in academia it is not consistent, and so not considered a reliable source... (which means they can't use it to cite stuff for college papers). Personally I appreciate you are into the etymology, and can look for my own source to verify. Thank you for taking up your time...
uomo comes from Latin homo, pl. homines, a third declension noun (declension = noun conjugation class) but the 3rd declension pl. -es ending was replaced in Italian by the originally second declension pl. ending -i, as in canus (dog), cani (dogs). Basically Latin had 5 declensions, and as it developed into Italian, 2-5 were all merged into 2, becoming the masculine, and 1 became feminine (so for 'girl', the Latin was puella sg., puellae pl., as in Italian ragazza, ragazze).
Basically, the extra bit in the plural is a relic from the Latin root.
(P.S. I suspect actually the fate of the Latin 5th and 3rd declensions is probably a bit more complicated than I've described here, but I'm no Italian expert(!), and it serves to demonstrate the point here at least.)
"siamo" means "we are"; "sei" means '"you are". We use the same verb in English and therefore need the we/you pronoun; the pronoun is optional in Italian because the verb already carries the we/you meaning. So siamo and sei both translate to 'are', but one is for 'we', and one is for 'you'.
I'm very confused because in some sentences for example "they are women" the traduction is Sono Donne but in another one it says "They are boys" and the traduction is Loro sono ragazzi so my question is Why sometimes the pronom doesn't appear even when the meaning of both sentences say the same?
Subject pronouns are optional because the conjugation of the verb indicates who does what. "Loro sono donne" and "sono donne" mean the same thing. This would be pretty confusing in English because "(we) are women" and "(you) are women" would look the same... but in Italian we and you have different conjugations.
Not all the italian words have the accent on the penultimate syllable (paroxytone words), although most do so. There are also words with the accent on the last syllable (oxytone words) and words with the accent on the third to last syllable (proparoxytone), such as "uomini".
Actually, you may even encounter words with the stress on the fourth from last syllable...we call them "bisdrucciole", but they are very rare.
I believe the plural of "uomo" is irregular (uomini) because this word comes from the Latin "homo" (whose plural is "hominis"); if the Italian is based on Latin, it isn't none surprise. (If in this text anything be wrong, correct me because I'm Brazilian, I speak Portuguese.
No. -Siamo uomini- and - Noi siamo uomini- have the same meaning. The subject (-Noi-) is implicitly assumed. It is not mandatory to write the subject pronoun in an italian sentence, unless you want to give some particular effect. They slighlty differ only in conversation if you want to underline something...
That's not unusual at the beginning. You'll get used to it in time. Try listening several times and use the slow version too. "uomo" is a particularly strange word, anyway. Also on other sentences very often there is a voice over for more practice. See here for some tips and very good Guidelines which you should keep handy.