There is none
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> As it is a method of communication, can it be taken as a language?

Nope. Thieves' Cant is a class feature, not a language.

> is it mechanically equivalent to something

Nope. Thieves' Cant is a [unique][1] class feature. Even spells like [Comprehend Languages][2] do not allow you to [understand Thieves' Cant][3].

> Are there any other rule mechanics e.g. background, that could grant Thieves' Cant?

Nope. With the DM's approval, only custom backgrounds or homebrewed class archetypes can give Thieves' Cant. There are no "official" ways to get this feature other than taking a level in Rogue. 

Although you can easily homebrew one
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Lore-wise, Thieves' Cant is a steganography. It allows you to conceal a secret message in your convenient speech. In other words, it is the skill to hide secret messages in whatever language you are currently speaking (thanks @guildsbounty).

Rules as written, a DM can allow Thieves' Cant as a custom *background feature*. See the PHB page 125 "Customizing a background":

> *If you can't find a feature that matches your desired background, work with your DM to create one*


  [1]: https://rpg.stackexchange.com/questions/53898/
  [2]: https://www.dndbeyond.com/spells/comprehend-languages
  [3]: https://rpg.stackexchange.com/questions/115608/