It should be little surprise, given a moment's thought, that distinct Cybertronian languages exist. The Transformers did not go about speaking English or any other known Earth language long ages ago on their distant metal world. Though the records of such conversations are frequently translated for us, we should not forget that these conversations originally evolved from dense code streams transmitted from one simple robot to another in the vacuum of Cybertron's surface and not primitive guttural monkey noises our own languages spawned from.
Marvel Generation One comics
Jazz made the statement that his real name was unpronounceable in English.
The Transformers cartoon
The first language used by the Transformers was likely the Quintesson language inherited from their former masters. It can be seen upon the walls of the Quintesson dimensional transporter room. It rather resembles Egyptian hieroglyphs — possibly a nod to "ancient astronaut" theories.
Ancient Autobot was the language used by the ancient Autobot colonists that fled Cybertron in the distant past. This was the probable precursor to modern Cybertronian dialects, probably as hard to read as Latin or Sumerian even to most modern Transformers (or at least the Decepticons) could not read it. This is later referred to as the language of the Primes.
In contrast, the language used by the Autobots when they first awoke in 1984 was easily learned. Spike Witwicky learned to read Modern Autobot after only knowing the Transformers for a single day.
See also Vok symbols.
Robots in Disguise cartoon
Rather unique to this universe, several Transformers (notably Optimus Prime and Megatron) have Cybertronian words etched onto their heads, near the cheek area. What they say is anyone's guess. (One theory is that they are simple function tags like "heat exhaust, crush danger and data pathway")
The writing on the All Spark itself should be given special consideration. Since it is the precursor to all life on Cybertron it stands to reason the first alphabet and syntax for the whole race is encoded on its sides. The All Spark was covered in Cybertronian glyphs, leading Sector Seven to conclude a connection between the All Spark and Megatron. Additionally, cometary forms are covered in Cybertronian "tribal markings".
The Decepticons communicate in Cybertronian (which to human ears sound like a collection of vowel-intensive electronic noises and rumbles... with the notable exception of Frenzy, who has a very staccato manner of speaking) when speaking among themselves on Earth, but have learned enough English to communicate with the humans when necessary. The crew members of the vessel Ghost 1 thought that one could make out words if they had a degree in theoretical physics — and were tripping on bad acid.
Cybertronian languages appear to contain a lot of information in small fragments.
It is also worth noting that this is the first time that Transformers are seen speaking their own language in any media.
There are also two versions of Cybertronian used in the AllSpark Wars Mini-ARG (Alternate Reality Game.) These are recycled versions of Ancient Autobot from "Cosmic Rust" and Decepticon from "Decepticon Graffiti!". They retconed a canonical order to both languages, based on fonts created by Jim Sorenson in the late 1990s. The Autobot Agoracer posted in Ancient Autobot, while the Decepticon Agoraptor posted in Decepticon. Both are available for download here under the names "Ancient Autobot" and "Decepticon Regular."
Doubtless Cybertronian split into two dialects due to the schism between Autobots and Decepticons. Autobot probably spoke in a poetic artisan dialect (e.g. Italian, French) and Decepticons used a terse militaristic form (e.g. German). Though both sides can understand each other and probably use similar base symbols (door, energon, alloy) higher terms are divided Autobot Glyphs include (hope, truth, defend) whereas Decepticon Glyphs used (murder, annihilate, pillage)
Universe 2008 "Classic Series"
The packaging art for many of the "Classic Series" toys in the 2008 Universe line features movie-like "tribal markings" on the characters, going along with the more movie-like renditions of the characters.