Does casting Tongues on the tarrasque (a language-less monstrosity) let it understand language?

Question

Tongues description:

This spell grants the creature you touch the ability to understand any spoken language it hears. Moreover, when the target speaks, any creature that knows at least one language and can hear the target understands what it says.

It specifies that creatures hearing the target must speak at least one language, but does not specify that the target must. To me that seems like an exception that proves the rule, so I think Tongues can effectively be used like Speak With Animals, but on any one creature at a time (instead of all beasts).

Does that ruling seem consistent with other rules related to creatures that understand no languages?

This specifically came up because I'm planning a RAW-as-possible level 20 fight against the legendary tarrasque, and one of my players suggested they should cast tongues on it.

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_{Related, but doesn't address Tongues spell: Do either Speak with Animals or Awakened Mind let me use Command on animals?}

Answer 1

The tongues spell works on any creature, with no restrictions

The tongues spell states:

This spell grants the creature you touch the ability to understand any spoken language it hears. Moreover, when the target speaks, any creature that knows at least one language and can hear the target understands what it says.

No part of this spell requires that the target creature be able to actually speak. In fact, it says you simply touch a creature, and when it speaks something happens. It never states that the creature must actually be able to speak. Thus any creature, whatsoever, including a Tarrasque, is a valid target for the spell.

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Note that the Tarrasque is a 3 Intelligence monster of complete destruction and it will be up to your GM how this plays out:

[...] The destructive potential of the tarrasque is so vast that some cultures incorporate the monster into religious doctrine, weaving its sporadic appearance into stories of divine judgment and wrath.

Legends tell how the tarrasque slumbers in its secret lair beneath the earth, remaining in a dormant state for decades or centuries. When it awakens in answer to some inscrutable cosmic call, it rises from the depths to obliterate everything in its path.

Furthermore the tongues spell does not actually grant the Tarrasque the ability to speak, and as it has no listed languages, whether it can speak at all will also be left up to your GM.