Learn Portuguese (Portugal): Ela insiste em pagar o jantar.

In Portuguese, certain verbs always pair with specific prepositions. The verb insistir (to insist) is always followed by em. You just have to memorize the pairing insistir em, even though in English we say "insist on".

Why is it pagar (to pay) instead of a word ending in -ing, since the English translation is "paying"?

In English, we use the -ing form (gerund) after a preposition, like "on paying". In Portuguese, you must always use the infinitive (the dictionary form of the verb, like pagar) immediately after any preposition.

Where is the word for "for" in pagar o jantar?

In English, we say "pay for" a thing, but in Portuguese, the verb pagar connects directly to the item you are buying without a preposition. You just say pagar o jantar (literally "pay the dinner"). However, if you are paying a person instead of an item, you do use the preposition a (for example, pagar ao empregado).

Why is there an o before jantar?

In English, we often drop the "the" for meals, saying just "dinner" or "breakfast". In Portuguese, nouns for meals generally require a definite article, so it becomes o jantar (the dinner).