Science fiction has a tendency to regard telepathy as a realistic mental ability that other species may have or humans may learn to develop in the future. This post lays out some fresh ways to write about telepathy based on how it might actually work.
Note the faith some science fiction seems to have in the future reality of mind reading, even though there is no clear theory on how it would work. I suppose being in physical contact with someone and picking up the energy from the electrical patterns of their mind, their brain waves, could form a theory of sorts that supports telepathy.
However, note that brain waves give an overall impression of a mind and do not at all reveal individual thoughts. In fact, they scarcely reveal individual emotions. They show the difference between a healthy and unhealthy brain and whether or nor someone is agitated, deep in sleep, drowsy, or normally alert. (It might be interesting to create a story where someone has the natural ability to read someone else's brain waves, but is only able to gather the broad information from so doing that I just mentioned.)
But even if we are to say telepathy works, because it just does, even though we don't know how, we also must deal with the fact that science fiction tends to regard the ability to read minds as a form of universal translator. If you can't speak an alien's language, all you need to do is make direct mind to mind contact and ta-da! you have solved your language problem.
I don't see why this would really work if reading minds were actually possible. For myself, I do a considerable amount of thinking in English and some bits of thinking in other languages, usually French or Spanish. Telepathy is not going to help you understand the words passing through my mind unless you know these languages in advance. Right?
You could suggest that if I were to deliberately think in mental images or if we were to deal with another mind that naturally thinks in images, then telepathy would allow you to understand what someone else is thinking, right? Um, not necessarily, because you may not associate the same ideas with the same images as your subject. And what if some of the images were of written language or other specific symbology? Would I automatically understand a scientist from China thinking words in Chinese script, even though I'd never studied it (or specific mathematical formulas I'd never studied)? Certainly not, though I might have an inside clue on the meaning of these symbols through picking up on how the subject feels about them. At best, if I had a way to perfectly memorize or record my telepathic experience, I could puzzle over the meaning of the message I'd received from another mind and perhaps figure it out in full eventually.
(Please recognize that when I talk about reading another mind, I'm talking about sharing the conscious thoughts of another mind. Sharing all possible things another person knows, the full subconscious, is not something a person even does with himself or herself, let with alone someone else. Being able to know everything a person knows would the equivalent of downloading another brain in its entirety, not telepathy.)
I realize some science fiction stories have included mind to mind contact with aliens and have portrayed it as an inherently difficult thing (e.g. Orson Scott Card's Ender's Game). Let me recommend taking that sort of approach to mental contact and broadening it. It makes sense that people would walk away from any telepathic experience, even with a member of their own species, not entirely sure of the meaning of the mind link they just engaged in (unless they linked with someone they knew very well). Needing to think over the experience after the fact and puzzle together its meaning goes naturally with the notion of telepathy, if you consider what stepping into a mind other than your own would really be like.
Note also that especially with alien species, there is no reason to think another mind would even process images in the same way as your own mind. I mean someone could directly tap into another mind and find what you believe is red is actually green in the mind of the alien and what you would call yellow is purple, what you would consider the bottom of an image is the top and vice versa, to give just a few examples of how other minds could process information differently. You could study the images you received and figure them out eventually--or you could study in advance to learn how other minds operate, training yourself with the ability to process images or sounds or whatever differently from how you normally do (or in some stories, this ability could be downloaded electronically). This kind of "brain training" would be very much like language training. A telepath would be required to study the internal software, i.e. the "languages," of other brains in order to communicate with them effectively. There might in fact be quite a number of standard ways a human mind works if you could read each one directly--and of course alien minds could be expected to work in entirely different ways.
It could be that a realistic view of telepathy would be that it requires every bit as much study--perhaps more even--than being a linguist. Imagine a story in which being a "licensed telepath" requires a PhD--in fact a story could focus on damage to understanding being done by someone with telepathic powers pretending to have training he or she didn't really have. Or pretending to know and understand more than telepaths can actually know or understand, because reading another mind would always be at least partially an art versus a science.
In fact a story could make this even harder--the general study of other minds could prove to be too broad. Most telepaths in such a story would only be able to master one or two other types of minds, even with the help of information directly downloaded into their brains from some kind of neural net. So you'd have to keep a horde of highly trained specialists in telepathy around in order to deal with a wide variety of minds too alien for linguistic communication...