Most commonly, the word is used to describe food. It can be used as an adjective or as an adverb:
NL: "Dit brood is erg lekker."
EN: "This bread is very tasty." (Lit. This bread is very [lekker].)
NL: "Ik heb lekker gegeten."
EN: "I very much enjoyed the food." (Lit. I have [lekker] eaten.)
Often, it's used to describe relaxation, decadence, or a pleasant atmosphere:
NL: "Ik lig hier lekker in het gras."
EN: "I'm lying here in the grass, and enjoying myself." (Lit. I lie here [lekker] in the grass.)
NL: "Het is lekker weer vandaag."
EN: "The weather's nice today." (Lit. It is [lekker] weather today.)
NL: "Ik blijf lekker thuis vandaag."
EN: "I'm taking a day off today." (Lit. I stay [lekker] at home today.)
NL: "Lekker toch?"
EN: "Good for you!" (Lit. [lekker] right?)
It can be used to describe health, and physical or emotional comfort:
NL: "Ik voel me niet lekker."
EN: "I feel nauseous." (Lit: I feel (me) not [lekker].)
NL: "Na het bad is de hond weer lekker schoon."
EN: "After its bath, the dog is nice and clean again." (Lit. After the bath is the dog again [lekker] clean)
NL: "Ik voel me lekker hier, bij deze mensen."
EN: "I feel at ease here, with these people." (Lit. I feel (me) [lekker] here, by these people.)
NL: "Ben je wel helemaal lekker?"
EN: "You must be mad!" (Lit. Are you fully [lekker]?)
The word sometimes has a distinctly sexual meaning:
NL: "Je bent zo lekker."
EN: "You're so sexy." (Lit. You are so [lekker].)
NL: "Zij is een lekker wijf."
EN: "She's a hot chick." (Lit. She is a [lekker] chick.)
But can also be used to describe young children in a casual manner:
NL: "Wat een lekker mannetje is jouw zoon."
EN: "Your son is such a fun/jolly kid." (Lit. What a [lekker] little man is your son.)
And can be used for sarcasm:
NL: "Nou, lekker makkelijk is dat."
EN: "That seems really hard." (Lit. Well, [lekker] easy is that.)
NL: "Nou, lekker hoor."
EN: "Ew." (Lit. Well, [lekker] hear.)
Overall, it's an incredible versatile word, and it's very common in everyday conversation. I don't think I've ever seen anything similar in any other language.
Are there any words in the indogermanic language family that could correspond to this? German "herrlich" comes to mind, but that word is better translated with the Dutch "heerlijk" (which is similar to "lekker", but isn't nearly as versatile).
What would be the best translation(s) of "lekker" into English, French, Danish, and into other languages spoken in countries close to the Netherlands? What about different language families altogether?