Arrival has an excellent exploration of this.

If someone has tech to do interstellar trips in a reasonable time, we already lost any war against them.

The good news is, they probably don't need anything that we have, so the list of reasons to engage in war is kinda limited. Yay!

About communication, they would have an advantage understanding us, we are broadcasting into space for more than a century with radio signals carrying content of many of our languages.

The movie Arrival does an quite OK job showing how could be an effort to bridge the communication gap with aliens (besides the fiction), and is a good movie as well.

It's highly unlikely that any intelligent species capable of traveling the vast distances to cross interstellar space to make contact with another species would not also be intelligent enough not to make knee-jerk assumptions about the language(s) of creatures who are so alien to them that they don't share a biosphere and have no ancestral commonality whatsoever. Even if the English word "the" sounds similar to the alien word for "let's fight," or whatever, they'd obviously know that this is not actually what we mean.

This is even assuming that they communicate verbally or even audibly in the first place. Maybe they talk by emitting light or radio waves at each other or something, for all we know.

And if the aliens arrive here with the intent of conquering us or blowing us up, they probably won't care what we have to say nor how we say it anyhow. If they were intent on making peaceful contact they would be sending their very best of their equivalents of linguists and anthropologists specifically because of this kind of thing. Not to do so would be incredibly stupid.

(Stupid species don't achieve interstellar travel. See also: We have not achieved interstellar travel.)

Why would Aliens desire war with us?

The book Project Hail Mary explores some interesting ideas about how we could communicate with aliens.

There are core concepts that are likely to be universally understood.

Maths is probably the best and most common example. If we imagine the symbols have been removed and we work under the assumption that we're manipulating objects we can show that 1 object + 1 object = 2 objects without any language necessary. From there we (aliens and humans) can work together to build a common foundation of understanding.

Don't get me wrong, this will not be easy and there will be problems we haven't thought of but there's a good chance that a spacefaring civilisation will know enough about mathematics to build a new common language.

One way to look at this is to consider why the aliens came in the first place. There's some common sci-fi tropes around this, but most of them fall apart under scrutiny. Now, this scrutiny does assume that our understanding of the physical laws of the universe are "close enough" that we can rule out such magic as stargates, warp drives or the like. Yes, there are some theories like the Alcubierre drive, but those sit far enough at the edge of "might be possible" that I'm going to ignore them.

Give us your resources (water, gold, hair)

On the scale of "everything in our solar system", the Earth contains a vanishingly small amount of everything which isn't biological. Water, minerals, and other inorganic stuff is in vast abundance in comets and asteroids. And this ignores the possibilities of rocky bodies much, much, much closer to home for any alien species. The distances in interstellar space are absolutely vast. Just getting to the next star over is going to require an insane investment of time, material and energy. And then you want to stop, turn around and go back? XKCD did a What If a while back which contemplated catching up to the Voyager probe and bringing it back. It's technically possible. It would also require something like 10-15 Saturn V rocket's worth of fuel. Now multiply that by a stupidly large number for going to another solar system. The energy expenditure to go pick up rocks in another solar system is just never going to be worth it.

And then there is the issue of time. Thanks to the wonders of length contraction, a vehicle could accelerate at 1G half way to the target solar system, flip around and decelerate at 1g to be able to stop there. And the time for the travelers would actually be pretty reasonable. You could cross the disk of the galaxy in about 24 years (assuming you want to stop on the other side) [source]. Of course, that's 24 years for the travelers. Back home a couple hundred thousand years will have passed. And you thought your dad has taken a long time to get cigarettes at the corner store.

Even just going to Alpha Centari , the traveler experiences 3.9 years. Back home, it's 6. This means there's a round trip time of 12 years, and that's just for the closest possible star. It gets far longer really quick. It's likely that hundreds or thousands of years will pass "back home" while the travelers are going somewhere. By the time they get back, their home may so radically different that the stuff they set out to get isn't even in demand anymore. Here is a fun calculator you can play with the numbers yourself.

The last thing to mention is the fun of Reaction Mass. Again, unless we find some spooky new source of thrust, going forward means throwing stuff backwards. And when you're talking about accelerating at 1g for years, that is an insane amount of "stuff" you need to huck out the back of your spaceship to keep that level of acceleration up. Once again, the scale of the universe results in insane requirements.

With all that said, strip mining nearby solar systems seems really unlikely. Perhaps more likely will be the next trope.

Hi, that's a nice planet you have there. It'd be a shame if someone colonized it.

So, this has all the "fun" of energy costs and reaction mass as above, but at least you don't have to worry about going back. And given the vast distances involved, this is a one way trip and communicating to the home world won't need to happen. It's going to be a case of launching a seed into the darkness and not expecting to hear from them again. Maybe provisions will be made to send back a "we did it" beacon. This will prevent reseeding the same planet over again. But, at a message latency of years (possibly centuries), keeping up a dialog is going to be pointless. Even a returning "we did it" probe could arrive back to a society which asks, "who the fuck are these guys?" Because all records of the trip got lost three centuries ago.

This is also something which is going to require a lot of faith on the part of the colonists. At best, the knowledge they have of the planet they are going to is years, decades or centuries out of date. Imagine getting part of the way there, only to realize that the planet you hoped to colonize got cooked by a large solar flare. You're now committed to a journey which will end with trying to desperately setup some sort of long term habitat somewhere really inhospitable. I hope you're good at creating O'Neill Cylinders. In fact, why didn't you just make one of those in the first place and save all the energy and effort of flinging yourself at a distant star on a wing and a prayer? Unless your home star is about to die, leaving it doesn't make much sense. Large rotating habitats are likely to be a far easier engineering challenge than building an interstellar ship. And they will be close enough to home that, if something goes wrong, help might actually reach them in time.

Our five thousand year mission is to seek out new life and explore strange new worlds

Ok, standard caveats here about energy costs and reaction mass. However, humans have done some pretty amazing things just for curiosity, aliens doing the same seems reasonable. Though this leaves the issue of time. Now, I'd expect that any such long range mission would be done with automated drones collecting data. Maybe with intelligent enough AI to recognize intelligent life, collect data and then start the long journey home. And maybe when it arrives home, it won't get blasted out of the sky as some unrecognizable alien device, because the program which launched it got shut down due to lack of funding 50 years ago. But, the time from launch to probe return starts to get kinda crazy really fast. Imagine you launch a probe and, if everything goes exactly right, it doesn't return for a thousand years. Maybe at some technological level this seems reasonable, but societies just don't seem to be stable that long.

So ya, maybe this would be a reason for automated drones recording anything and everything they can. But sending people to do this means those people leaving home and expecting to return to a world so vastly different from the one they left as to be unrecognizable. Unless they somehow have a society that just doesn't drift at all, it's quite possible that they will arrive home and have to figure out the language their own people are speaking. I don't doubt we would find people willing to take this on (heck, I might have gone for it when I was younger). At the same time, the investment of energy and resources will need to be borne by a society which has zero expectation of ever seeing anything back for that investment. Again, it's possible, but also seems pretty far fetched.

The great invisible sky wizard of Frobozz demands we cleanse the universe of the unclean (this means you).

Another thing, which has motivated humans to amazing heights of effort, wastefulness and stupidity is belief. Nothing gets large groups of people motivated to piss away resources like a religion. Why would it be any different for aliens? So maybe, there is some species out there which is majority held under a strong enough belief system that they are actually willing to expend the time, energy and resources to obliterate any signs of alien life. And Earth just fucked up by having an oxygen rich atmosphere. As a possible sign of life, this means all Earthlings must die. So, how are we destroying the Earth? Well, we could go there, look for signs of life, report back, setup an invasion fleet, etc, etc. Or, remember that whole "slowing down" part of visiting another solar system? What if we skip that and instead just send several large chunks of iron and have them keep accelerating the whole way? They can then use advanced Lithobraking to turn said planet to a far flung cloud of debris. This takes less time and avoids issues with plucky pilots flying up the exhaust port of our invasion mothership.

Welcome to the Dark Forest. Population: Whatever it was, less all humans. If the goal is total annihilation, the same tech which would get a ship to another solar system is exactly the same tech needed to simply destroy a planet in that solar system. At the energies involved in a sizable object moving that fast, it's going to exceed the binding energy of a planet. Fling a few such devices at a remote solar system, provide a bit of automated terminal guidance and program them to dust any planetary body which shows signs of life. Set a timer for a few years/decades from now to turn your telescopes that direction and wait for the show.

In this case, they won't care what our language is and we won't even know we've been "visited" by aliens, as we will have all died in massive flash of energy. Good times all around.

Conclusion

Unless there is a way around the speed of light limit to the universe, visiting other solar systems is probably off the table. Sure, there may be some very long range program to send automated drones to the nearest stars and collect some data/pictures for return to a later version of our society. But at the energies and timescales involved, it's unlikely. And for further away solar systems, the timescales make it so impractical that it's probably never going to happen. This also means that aliens visiting Earth and having to sort out our language, is also likely never going to happen. Getting out here just really isn't practical.

Everyone here assuming the aliens would be far more advanced than us.

Can't remember the author or title.

Old short story where humans land on a planet where the advanced species has gone extinct.

The Terrans have no way of translating the language until someone finds a classroom and figures out what they used for the periodic table.

if an alien race interstellar/intergaltic, wanted war, they communicate by starting blasting/orbital bombardment from space as a demonstration.

Think of it like this; we are not very different from humans 2000 years ago but the speed at which we can collectively decode a new language is several orders of magnitude faster now than it was back then. Thanks to technology that we collectively invented; same holds true for any civilization more advanced than us.

I would imagine that if an alien species is making first contact, they have a reason to want to communicate and would have prepared based on our broadcasts or would bring along a specialist to study our language quickly.

The other options would be an accidental contact, in which case they might not be as prepared, or a contact that they are indifferent about communicating with us, in which case we are likely fucked.”

Aliens have been helping us develop super intelligent AI to bridge the gap between our species