It's an interesting theory, though I think at best it's incomplete.

Someone with a deep pathology is liable to act out on that pathology in some way, and that can be destructive to a relationship, regardless of how much is communicated in one or all of these love languages. A common sort of way that might manifest would be infidelity: once discovered, it shatters trust even though the unfaithful partner was behaving in very loving ways before and after the affair.

I'd also suspect that there is more to building a good relationship than expressing love. You need to have some sort of common interest, something enjoyable that you do together. People seem to do things that are fun for both of them when they fall in love, and I'm not talking about sex (that's fun for everyone). And people who sustain relationships find some way to be compatible with things like moral issues, money, and life ambitions.

I wish I were perfect about these sorts of things, but then no one is perfect. So there is still one more thing that needs to be there: tolerance and forgiveness when one's partner doesn't live up to the ideals.

Mine is acts of kindness which includes quality time with me and touch. Words mean little to me without action. Gifts are nice but for me they need to have meaning. Again, the action or forethought behind them needs to be there.

I speak all of those, but it omits perhaps the most noble of any such hypothesied linguistics of Love

Self Sacrifice for the sake of the loved one

I speak all of them fluently. I teach a workshop on the subject. Lots of people have heard of the general concept, but are unaware of the theory of dialects. Which means that two people can speak the same Language and still not connect because they're speaking different versions of it.

The biggest predictor of the impending demise of a relationship, however, is contempt. Read up on John Gottman's research on Bids For Attention. The Love Languages fit in here in what people recognize as Bids For or Responses to Bids For Attention.

People can have misaligned Love Languages and still work things out. But once someone in a relationship reaches a contemptuous stage in the relationship, not only will compatible Love Languages not fix the problem, but the Love Language can actually become weaponized and be used against the other person.

That's not entirely true.
I've been in relationships where these same things were reciprocal and the relationship came to an end eventually anyway.

Fifteen years married to someone who hated to be touched. It eventually corroded our marriage to the point where we had a better relationship after we split.

I've come to realize how important this actually is for relationships. I'm a physical touch person, and if my partner doesn't speak my language, it's like we're not even together.