Italian is my mothertongue.
I know english pretty well - at least I hope so, any native speaker that knows me around the forums feel free to destroy my certainties about my language skills and tell me I actually suck - , thanks to Steve Harris mostly.
Actually, your English is very good. There are a few phrases here and there that are rather unidiomatic, but the meaning you intend is pretty clear. But, if you want to improve:
No, seriously, until I was attending school lessons, I was barely above the average grades, the bare minium.
I think "No, seriously, while I was in school, my grades were barely above average. I did the bare minimum." would be a better way to phrase what you intended. "until I was attending school" implies that this happened before you went to school. "school lessons" is a little redundant too, so you would drop the "lessons" here. "my grades were above average" would be better here, as the focus there is more on the grades than it is on you (if that makes sense). You should also avoid translating
sopra la media too literally there, as English would render it as "above average" rather than "above the average" (same goes for sotto la media).
When I discovered foreign and heavy music, I started to pay attention to the lyrics, trying to translate them and understand them better, and my english skills vastly started to improve.
I would not use vastly here (in general, English tends to eschew "descriptive" adverbs in favor of more specific verbs and adjectives). You could use:
"and my English was improving by leaps and bounds"
"and my English began/started to improve [by] a lot"
"and I began/started making big strides in my English skills"
etc.
Also, this sentence is a little long by English standards, so I would try to break it up into two sentences.
My initiation with foreign music was with Bon Jovi, but Iron Maiden are better to learn the language, that's why I jokingly credited Steve Harris.
No issues here.
By the last year of high school I was already known in the classroom as one of the best ones in english and to this day at work I'm the go-to person for english speakers (we are an italian support so people are supposed to speak italian, but once in a big while happens the english speaking customer and if I'm available, they let me talk to him).
"By the last year of high school, I was already regarded as one of the best English students." // "By the last year of high school, I was already viewed as one of the better English speakers." Would be better ways to phrase that, I think. "regarded" and "viewed" imply a certain degree of subjectivity here, while "known" sounds more objective to me (like I would use it more for stating facts). "in the classroom" is implied by "high school" here, so it's a bit redundant. "one of the best ones in English" doesn't sound very idiomatic, especially the last three words. Again, this would likely be broken up into several sentences:
"At work, I'm the go-to person for English speakers. We are an Italian support company/department, so people usually speak Italian, but every once in a while we'll have an English-speaking customer. If I'm available, they'll have me talk to them".
Notes on this:
"To this day," sounds a little formal, so I wouldn't really use it here.
Specify that it's a company or a department in a company. "A support" does not work in English.
"supposed to speak Italian" sounds a bit more...I dunno, aggressive? Nationalist? Basically, it sounds more opinionated rather than like a straight fact. "so people usually speak Italian" functions more like giving background information and is a bit softer. You could even cut that clause out, which could be phrased as: "I work [in an Italian support company] // [in a support company here in Italy], but even then we'll get an English-speaking customer every once in a while".
"but once in a big while happens the english speaking customer" has a few problems. "big while" isn't an expression that you would use in English. I guess the equivalent would be "in a long while", but that implies something that hasn't happened for a long time (e.g. "I haven't played Pokemon in a long while"). If you're trying to imply that this is an uncommon but regular occurrence, you would use "every once in a while". "happen" is also typically used more with verbs rather than nouns, so you would use "we have" instead. You
can use it with pronouns or proper names sometimes, but it has a negative connotation (e.g. "The house is a mess, what happened?" "The cat happened.", implying that the cat is the cause of the mess). You would also use "an" (the indefinite article) rather than "the" (the definite article), because there's an implication that it's an individual English-speaking customer.
Songs are to be credited for the little I know of german - I 've been in Germany many times, and I love the language, and while it's absolutely incorrect to say I know the language, I can recognize some words here and there, and also realize how the composite words are made up (you know how german can create a single, 25 letters single word by patching together three words.... I can recognize where one word ends and the other starts, most of the time).
Again, this would likely be broken up into multiple sentences:
"Music is to be credited for the little German I know. I've been in Germany times and I love the language, but it would be absolutely incorrect to say I know the language. I can recognize some words here and there, and and I can also figure out how some super words are made up (you know, how German can create a single, 25-letter word by patching [or gluing or sticking] three words together). Most of the time, I can recognize where one word ends and the other starts."
Most of the other issues here are very minor, and a lot of them I've covered before.
Also there are 2-3 german songs where I know the chorus, in the sense that I could sing along to the lyrics actually knowing what I'm pronouncing.
This one is a little less clear. You would either use "and I actually know what I'm saying", which implies you understand the meaning of the words you're saying, or "and I can recognize and pronounce some of the words".
For other languages, I guess I can vaguely make something out of french and spanish stuff. When I was in Spain I tried to speak english, but when people realized from the accent that I'm italian they tried to speak italian as well, so basically I spoke "fake spanish" with them - I was getting understood better when I was improvizing spanish words than when I was speaking english
"For other languages, I can vaguely make something out of French and Spanish. While I was in Spain, I was trying to speak English, but when people realized that I'm Italian from my accent, they tried to speak Italian. So basically, I ended up speaking "fake Spanish" with them. I was better understood when I was improvizing Spanish than when I was speaking English."
In general, I would say work on
optimizing sentence length and avoiding
run-on sentences. Also, remember that in English nationalities and languages are capitalized (I know they aren't in romance languages like French and Italian, so understandable error). In general, your grammar and verb conjugations are good. You have a good use of vocabulary and you correctly used some idioms and set-phrases. Those are probably the hardest things to learn in English, and unfortunately they're also the bread and butter of English lol. Wiktionary has a VERY comprehensive list of idioms and set phrases, but it's almost TOO comprehensive sometimes. Hope this all helps!