Rules As Written, having a low INT does not prevent you from communicating.
The designers of 5e have a saying: "The rules only do what they say they do. There are no secret rules."
There is no rule that says that you can't communicate abstract concepts if your Intelligence score is too low.
It's possible to write lots of arguments for why something should be true, but ultimately, if there's not a rule saying it happens, then you're just creating a house rule.
And house rules are great and can make the game more fun, but it's important to understand the difference between a house rule (which applies to your table) and an actual game rule (which applies to everyone's table).
The DM may choose to house-rule additional penalties for characters with very low INT.
Many DMs like to add additional rules to their game, to better model reality. This seems like the sort of rule that someone could add.
But it might be a bad idea.
It would be tricky to enforce this rule, because you basically have to start policing what your characters are/aren't allowed to say. Imagine:
BARBARIAN (polymorphed into spider): We should probably check for traps on that chest.
DM: Hey, you can't suggest that! You're not smart enough to think of it.
BARBARIAN: Um, I guess I didn't say that, then?
BARD: Well, I think we should check for traps on that chest. I've just gotten the idea for it.
DM: You can't say that either, because now you're just metagaming.
WIZARD: Okay, but I've got an 18 INT, so I definitely could think of it, and also I was just going to suggest it before the barbarian said it first.
DM: (grumbling) Okay, but I kind of feel like you're metagaming and lying about it.
I think a lot of the fun of D&D is in solving problems, so I try to stay far away from any house rule that would tell my players that their characters aren't smart enough to solve problems.
(In terms of practical experience: my players already say things sometimes like "my character isn't smart enough to think of that" and I don't like it and I wish they would stop.)
Characters with a very low INT score already get penalties from that: they get a low modifier on Investigation checks and on knowledge skills such as Arcana and Religion. I think that's enough of a penalty.