Had some spare time and did some thinking.
If you don't know the background to this already, there's a book
Home | The 5 Love Languages® | Improving Millions of Relationships? One Language at a Time. Maybe I haven't done enough of my own reading but it seems to me that there are TWO facets to each of those five languages. It's our responsibility to speak in a language other people understand to get our message across. There are TWO parts to language – speaking and comprehension.
If my partner, colleague, babysitter, etc doesn't understand Korean, I would not go around trying to initiate discussions or tell them anything important in that language. If they only speak Spanish to me, I would not understand anything they were telling me. If neither of us made an effort to use the other language, we'd never accomplish anything together.
This is where that Love Languages facet thing comes in. You have to be aware of what YOU use to demonstrate your love, and you also have to be aware of what you like to receive from your partner to internalize their love for you. You also have to speak to your partner about love in a language THEY understand, and recognize when they are trying to express love in THEIR own language. So for a good marriage, you need all FOUR of those things going.
If the man gives love through touch, the woman has to understand that him touching her and trying to initiate sex is not about his physical pleasure, it's about him demonstrating love. If the woman doesn't understand this, she just feels groped all the time and that he treats her body as a tool for him to use. She won't feel loved.
If the woman receives love through acts of service, she feels loved when her partner does his fair share around the house and extras for her. If the man slacks off on housework or tends to leave home reno projects unfinished, she won't feel loved.
If the woman gives love through quality time, she expresses her love by wanting to be around the man all the time, and wanting them to go everywhere together. If the man doesn't understand this, he just feels smothered and annoyed by her constant presence. He won't feel loved.
If the man gives love through gifts, he may frequently bring flowers, trinkets, appliances, chocolate for her. If she doesn't understand this, she may be annoyed at the expense of the flowers all the time, feel the knick knacks are cluttering up the house, think that appliances mean he wants her to work harder in the kitchen, and be disappointed that he's not supportive of her attempts to lose weight. She won't feel loved.
If the woman gives love through words of affirmation, she may always be talking about how great he is, how much she loves him, how she finds him attractive, etc, but he won't believe it if she doesn't follow it up with action that matches what he likes to receive. He won't feel loved.
If the man receives love through quality time, but his wife likes to keep busy with the house, the children and her job and hobbies, he will feel low priority in her life and feel neglected. He won't feel loved.
If the woman receives love through words of affirmation, but her husband tends to be uncommunicative and not talk about his emotions, she'll doubt his feelings for her. She won't feel loved.
If the woman gives love through acts of service, she may work hard to keep the house spotless and have gourmet dinner ready when he comes home from work. But if he loves simple mac 'n cheese just as much as roast chicken with all the trimmings and would prefer to unwind from work in front of the TV before eating, he won't feel loved.
I could go on and on with examples of love language incompatibility. Even the HD/LD divide (except when medical) is fundamentally a difference in the love language of touch. The HD person is one who gives AND receives love through touch, while the LD is someone for whom it's much further down on the scale. They simply can't understand the message, nor can they communicate well in it.
There's also an unfortunate dynamic where people feel that expressing love in a way that doesn't come naturally to them only needs to be done for a limited time. So if you need to receive touch, your partner may provide sexual activity long enough to prove they love you, then assume that now you know, those efforts don't need to be kept up. If you need to receive gifts, your partner may initially provide a sufficient supply to demonstrate their affection and devotion, then slow down or stop because you've been 'won.'
I think the best marriages must be those who have compatible love languages, where each partner likes to give the same thing their partner likes to receive. Anything else leads to resentment building up over time unless the partners put in great effort at communication.