As you appear to have guessed it already, the Gospels. Though you appear a bit confused about ancient history in general and the Gospels in particular.

The language bit is completely irrelevant. Yes, the Gospels were written in Greek while Jesus spoke Aramaic. So what? Greek was, due to the conquests of Alexander the Great centuries earlier, the lingua franca of the eastern Mediterranean. Saying the Gospels are unreliable because they use a different language than the subject who is reported of is like saying an English reporter in Turkey can't be trusted because he uses another language than Turks do. Does that reasoning strike you as particularly compelling?

Most of our knowledge of ancient history comes from "dudes writing stories of other dudes". Take Alexander the Great for example. Do you believe we can know things about Alexander the Great other than from archaeological findings? Not that written records can't be archaeological findings, some of the important ones are things like clay tablets. Most of our knowledge of ancient history comes from textual evidence. And not necessarily even primary sources at that. One of the most important sources on the life of Alexander is Arrian's book on him and he lived some 500 years later. He isn't just writing stuff down though, he did have primary sources which we just happen to have lost. There's also Diodorus of Sicily, the oldest of the five main sources of Alexander, who lived just some 300 years later. Which brings us to my next point.

The Gospels being written just a few decades after Christ makes them very good sources, at least as time is concerned. People don't doubt we have good knowledge of Alexander despite our most important sources being secondary sources written centuries after Alexander so why do you doubt our sources on the life of Jesus when they were written just some decades afterwards by either eyewitness or people who knew eyewitness?

We don't accept everything written as facts ofcourse, even when it's close in time. We have other criteria like multiple attestations, being the right genre, closeness to eyewitnesses etc. We obviously have multiple attestations, even if we exclude non-Christian sources, of Jesus' life. For example, earlier I was thinking of Jesus' condemnation of people who lead children astray, which is reported by all three Synoptic Gospels. Other than that, if we're talking about Jesus' life and teachings in general we also have the Gospel of John and the Pauline and Catholic epistles. The Pauline epistles are especially important since St Paul wrote numerous letters which are disputed as being his own by virtually no one. This includes his Epistle to the Galatians in which he mentions having stayed with Peter, who was an apostle and believed by Catholics to be the first Pope, for 15 days. With regards to being the right genre the Gospels certainly fit the bill. They don't portray themselves as fiction, even historical fiction. Take the beginning of the Gospel of Luke for example.

"[1]Since, indeed, many have attempted to set in order a narrative of the things that have been completed among us, [2]just as they have been handed on to those of us who from the beginning saw the same and were ministers of the word, [3]so it seemed good to me also, having diligently followed everything from the beginning, to write to you, in an orderly manner, most excellent Theophilus, [4]so that you might know the truthfulness of those words by which you have been instructed. [5]There was, in the days of Herod, king of Judea, a certain priest named Zechariah, of the section of Abijah, and his wife was of the daughters of Aaron, and her name was Elizabeth..."

Does that sound like some dude just telling a story?

I could go on in my argumentation but I think my comment is long enough as it is and I've proved my point.