Learn French: Il y a longtemps que cet expatrié étudie la langue. - This expatriate has been studying the language for a long time.

In French, when an action started in the past and is still going on right now, you use the present tense. Because the phrase Il y a longtemps que establishes the ongoing time frame, the present tense verb étudie translates naturally to "has been studying" in English.

Could I use Ça fait longtemps que instead of Il y a longtemps que here?

Yes, absolutely! Ça fait longtemps que and Il y a longtemps que mean exactly the same thing when talking about how long an ongoing action has been happening. Ça fait... is just a bit more common in casual, everyday spoken French, while Il y a... is slightly more formal.

Is longtemps one word, and could I say un long temps instead?

Longtemps is a single adverb meaning "a long time" or "for a long time." You shouldn't translate "a long time" word-for-word as un long temps; French speakers almost always just use the single word longtemps.

Why is it cet expatrié instead of ce expatrié?