Learn Portuguese (Portugal): O professor vai para Londres trabalhar.

In Portuguese, both a and para can mean "to" when talking about direction. We use para here because it implies moving somewhere for a longer time or for a specific life purpose, like moving to London to work. If the teacher were just going on a short trip, we would use a instead.

Why is trabalhar at the very end of the sentence?

In Portuguese, when you state where someone is going and follow it directly with an infinitive (unchanged) verb like trabalhar, it automatically acts as the reason for the trip. It translates to "in order to work" or "to work". You do not need to add any extra words between the destination and the action.

Why isn't there a definite article before Londres?

Most cities in Portuguese do not take a definite article (like "the") before their names. Because Londres (London) is one of these cities, we just use the preposition para on its own, rather than combining it with an article.

What verb is vai from?

It is from the highly irregular verb ir, which means "to go". Because the subject is O professor (a "he"), we use the third-person singular form, which is vai.