Learn Hardcore Japanese: saikin gaikokuzin ga huete imasu. - Recently, the number of foreigners is increasing.

最近 (さいきん) is an adverb meaning “recently.” In Japanese, time expressions or adverbs normally come before the verb or clause they modify. By putting 最近 at the start, the speaker sets the time frame right away: “Recently, [this action] has been happening.”

Why is the particle が used after 外国人 instead of は?

が marks the subject and is often used to present new or neutral information. Here, “foreigners” is the thing that’s changing. If you used は (“外国人は増えています”), you’d be making “foreigners” the topic and potentially implying a contrast (e.g. “As for foreigners, they are increasing [but something else isn’t]”). が keeps the statement straightforward: “Foreigners are increasing.”

Why is 増える in the ～ている form (増えています) rather than the plain form?

The ～ている form with intransitive verbs like 増える expresses either an ongoing process (“are in the process of increasing”) or a resulting state (“have increased and remain at a higher level”). English uses both “are increasing” and “have been increasing.” Japanese wraps both senses into 増えています, showing that the increase is happening and its effects are still in place.

What exactly does the ～ています ending add compared to just saying 増える?

増える (dictionary form) can mean a habitual or future action: “(They) increase” / “(They) will increase.”
増えている highlights that the action is happening now or that its result persists: “(They) are increasing” or “(They) have increased.”
So 増えています adds a nuance of continuity or current relevance that plain 増える lacks.

Is 増える a transitive or intransitive verb? Why does that matter?

増える is intransitive (“to increase” on its own). Intransitive verbs describe something happening by itself, so you mark the doer/experiencer with が. The transitive counterpart is 増やす (“to increase something”). When you use 増やす, you’d typically see を marking the object you’re increasing.

Are the commas in 「最近、外国人が増えています。」necessary?

No, Japanese commas (、) are largely optional and serve only to show a natural pause or separate elements for clarity. You can write it as:
「最近外国人が増えています。」
Either way is fine; adding a comma after 最近 just mirrors how you might pause in speech.

Could we switch 外国人が to 外国人は? What changes?

Yes, you could say 「最近、外国人は増えています。」 but the nuance shifts. With は, you’re setting “foreigners” as an established topic—often implying contrast or that you’ve already been discussing them. It would sound like “As for foreigners, they are increasing,” perhaps contradicting or comparing to something else. Using が keeps the focus on presenting the fact of their increase.