So one of the Paladins did a find steed spell; got a Celestial Raptor (think Jurassic Park - ol' Blue).

Now the parts of the spell I am going to ask about -

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Additionally, if your steed has an Intelligence of 5 or less, its Intelligence becomes 6, and it gains the ability to understand one language of your choice that you speak. - He gave it Common

While your steed is within 1 mile of you, you can communicate with each other telepathically.
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The DM put the Intelligence at 6.

The Paladin was not with the party (didn't want to go into the area) - but sent their mount.

The party was having a discussion about a parchment they found with an ancient language.

The party was trying to figure out if any of them recognized it (History Checks).

Now would the Raptor (in your view) be able to convey an Ancient Language (think like some old Myan language) back to the Paladin to see if the Paladin could make a History Check to know if he knows it (since he can't visually see the runes on the parchment) and the Raptor only is able to communicate in Common (even if the Raptor is speaking telepathically - unlike Familiar, the Paladin can not see through the Raptor's eyes to see the parchment).

I’d say no. In the example, you are talking about reading something, and understanding a language is not the same as reading it. 
And beyond that, I don’t think I’d allow a sort of telephone game translation. I just think, if someone was speaking a language I didn’t know, and I tried to mimic the sounds they made, it would not come out right. The accents would be off, and my mouth just isn’t used to making those sounds, so I’m sure I’d mispronounce enough words that it would be unintelligible.

Quote from Kotath >>

If the Paladin is within a mile, then it depends on whether the telepathy allows conveying of images. However a mile is not very far and the paladin is likely not that close. And the telepathy can likely only handle text style thoughts.

I wouldn't allow it in a more RAW game, and in a more Rules as Fun game that horse is going to be rolling at a severe penalty.

Just because it's celestial/fey/fiend in nature, it's still a "horse".  All of the monsters with Find Steed have a natural Int of 2, except for the Mastiff at 3, and then get bumped to 6.  They don't gain knowledge at all, they don't gain understanding(except the language given by the spell), so the subelties of being able to convey that language would be totally beyond the Steed.  It could convey things such as "They found this paper with funny writing on it", and IF one of the PCs that was there could identify what it was, the steed could then communicate back to it's PC that hey, this is there.  But then what?  How is the horse going to accurately be able to convey what it's seeing?  A -2 Int check?  Now, if the players could accurately roleplay out them describing the image to the player, the player draws it out and it is correct?  **** it, you know what, that's just good fun and you if you have history trained I'd give it to you.  No roll required, because you did it in real life.  

Even with the communication clause, I can't really think of anything that has telepathy that allows the users to share full form ideas or images at what is essentially 5th character level or lower.  

When thinking of rulings, I always try to consider either magics available at that level that would possibly allow what the player is thinking, or if there are spells at higher level which have the same type of allowances(communication over long distances), what limiations are based on them.  The cantrip message has some severe distance requirements, and the 3rd level sending spell, which while achieveable at level 5 is also a higher tier of magic than the 2nd level Find Steed, has unlimited distance but a limitation on words.  The 5th level spell Dream kind of lets you give images to other players in the form of dreams, being able to form that image as part of the dream and the PC then recalls it perfectly, but that's the lowest level magic I can think of that allows that.

Based on all of that, RAW, the horse isn't going to be able to send images to its Paladin.  

Yeah - right, as of now - I am ruling their telepathic communication to essentially be one way (Paladin to Mount and the communication from Mount to Paladin is basic - as in acknowledging the commands it hears telepathically).

The Raptor is capable of hearing/obeying the Paladin's commands for up to one mile; but the Raptor doesn't mentally communicate back anything other than basic thoughts of "On my way" type commands.

So if the Paladin falls in a pit, he might say, "Ms. Claws, fetch me the rope in my bag on the edge!" and the Raptor could go grab the rope and shake it's head and lower it down, for example. But it wouldn't be able to tell the Paladin, "Hey there's two goblins standing by your bag. I need to kill them first. Give me a second." Or even show that there's two goblins standing by the bag. (Just made up examples).

Quote from SirTawmis >>

Yeah - right, as of now - I am ruling their telepathic communication to essentially be one way (Paladin to Mount and the communication from Mount to Paladin is basic - as in acknowledging the commands it hears telepathically).

The Raptor is capable of hearing/obeying the Paladin's commands for up to one mile; but the Raptor doesn't mentally communicate back anything other than basic thoughts of "On my way" type commands.

So if the Paladin falls in a pit, he might say, "Ms. Claws, fetch me the rope in my bag on the edge!" and the Raptor could go grab the rope and shake it's head and lower it down, for example. But it wouldn't be able to tell the Paladin, "Hey there's two goblins standing by your bag. I need to kill them first. Give me a second." Or even show that there's two goblins standing by the bag. (Just made up examples).

So the Goblin piece?  The PHB 2018 Errata changed it to "Communicate with it" to "Communicate with each other".  It's also now an intelligent creature.  It might not be bright, but it'd totally be able to go "Hey, that's my Masters pack and those aren't his friends, let me tell my master."  The steed might not know they are goblins, or how to describe goblins(at first anyway, once its seen it, it should know), but Animals have an intrinsic sense of defense.  Dogs are a great example, they will protect your property if you train them, and they'll grow to recognize your friends but still be hostile to randoms in the right situation if that is what their training dictates.  

Right, the intent behind bringing up dream was to show that while it can give some mental imagery, its also a much more powerful magic spell, so that kind of makes sense.  You can also use dream on willing creatures to impart knowledge.  Dream allows you to cast it on someone else to act as the messenger to enter someone elses dream.  Have a character who took the Keen Mind feat?  Cast dream on them to act as the messenger, and then have them enter someone elses dream to give them directions/purpose of where they were.  Now that character has great mental images of what happened, not just second hand knowledge. 

To your points, those are DM fiat.  Like the Raptor in this scenario, the DM has to allow it.  Even conjuring a spirit with an INT of 6.....it still has an INT of 6.   The earlier editions point is also not relevant here, this is 5th edition.  Spells do what they say they do, nothing more or less.  This doesn't say anything about the "horse" being more than just a conjured mount, other than the communication piece and the slightly increased intelligence.  It doesn't suddenly become an intelligent creature rivaling a PC.  

Agreed - to me, it's like a Celestial version of Lassie.

Like Lassie was a really smart dog. Knew when her pet human was in trouble. Knew to go get help and often where to get help.

But couldn't run to the cops and say, "Hey, Timmy fell down the well." It'd tug at their sleeves and bark and give a sense of urgency.

I figure the bond to the Paladin might allow it to communicate basic ideas, "I will fetch help", "I will attack the creatures by your bag", but not be like, "Hey, your party members found a parchment with these ancient runes - three lines run to the left, one down, six across, there's a circle in the middle, three eyes above a pig - do you think you can figure out what language that is, pet human?" :)

I feel like this would really only work if this was written using the Common alphabet but the words written are in another language. I know that several languages in D&D are called out as being written with Dwarven Script, although the languages are completely different.

My correlation to dream was all about how it can be used for imagery. Nothing more. You have spoken of it in a purely offensive state, I haven't. We are speaking around each other. 

Further, I never made that assertion. I'll no longer be continuing this tangent with you in this thread. 

Quote from Spideycloned >>

  I'll no longer be continuing this tangent with you in this thread. 

I agree this is beyond the abilities of the raptor. I would also question the situation in the first place. A paladin "not wanting to go into an area" but sending his steed anyway as a proxy just feels like they're trying to turn it into a way to be in two places at the same time. Find Steed is not Pact of the Chain warlock.

Quote from SirTawmis >>

Yeah - right, as of now - I am ruling their telepathic communication to essentially be one way (Paladin to Mount and the communication from Mount to Paladin is basic - as in acknowledging the commands it hears telepathically).

The Raptor is capable of hearing/obeying the Paladin's commands for up to one mile; but the Raptor doesn't mentally communicate back anything other than basic thoughts of "On my way" type commands.

So if the Paladin falls in a pit, he might say, "Ms. Claws, fetch me the rope in my bag on the edge!" and the Raptor could go grab the rope and shake it's head and lower it down, for example. But it wouldn't be able to tell the Paladin, "Hey there's two goblins standing by your bag. I need to kill them first. Give me a second." Or even show that there's two goblins standing by the bag. (Just made up examples).

 Jeremy Crawford tweeted the communication between the Paladin and mount is meant to be two-way, so they can both talk to eachother vs just Paladin commanding the mount.