Loop through attributes in the custom validation method

I want to loop through attributes which are validated with custom validation method. I have model Post which has_many :languages and a model Language which belongs_to :post. In the languages table I have columns - id, post_id, language.

Post model:

class Post < ApplicationRecord
  has_many :languages

  accepts_nested_attributes_for :languages, reject_if: :all_blank
  validates_associated :languages
end

Language model:

class Language < ApplicationRecord

  validate :unique_languages?

  def unique_languages?
    #LOOP ATTRIBUTES
  end
end

IIn the Language model in the unique_languages? I want too loop through all language attributes of the post. This is posts_controller with strong params and logic for creating a post:

class PostsController < ApplicationController

  def new
    @post = Post.new
    @post.languages.build if @post.languages.empty?
  end

  def create
    @post = Post.new(post_params)
    @post.languages.build if @post.languages.empty?
    if @post.save
      redirect_to action: 'new'
    else
      render 'new'
    end
  end

  private

  def post_params
    params.require(:post).permit(:title, languages_attributes: [:language])
  end
end