There's a Japanese class in my town, and I go to the class as a volunteer.

Usually, around ten foreigners come to study Japanese, but if it's rainy lesser than usual if it's raining.

The two Americans are English teachers in the nearby town.

Last week 12 Vietnamese came and we havpeople came meaning we more than doubled inthe size of the class.

Usually, around ten foreigners come to study Japanese, but if it's rainy then there will be lesser than usual.

The two Americans are English teachers from a nearby town.

Last week 12 Vietnamese came and we have more than doubled in the class.

There's a Japanese class in my town, and I go to the class as a volunteer there.

Usually, around ten foreigners come to study Japanese, but if it' is rainy lesser than usualing then fewer people show up.

Sometimes, there can bare only four or five students.

The two Americans are English teachers from a nearby town.

Last week 12 Vietnamese came and we havestudents came and so the class had more than doubled in the clasusual number of students.

There's a Japanese class in my town, and I go to the class as a volunteer.

I would say: There's a Japanese class in my town, where I volunteer.

Usually, around ten foreigners come to study Japanese, but if it's rainy, then it would be lesser than usualthat.

Sometimes, there can bewould only be four or five students.

The two Americans are English teachers in a nearby town.

Last week 12 Vietnamese came and we havestudents came, which more than doubled inthe size of the class.

Usually, around ten foreigners come to study Japanese, but if it's rainy lessthen fewer than usual.

Sometimes, there can bare only four or five students.

What you wrote is grammatically fine but native English speakers usually don't say "there can be" unless they think it is unlikely or possible, but has never happened before.

The two Americans are English teachers from a nearby town.

You can also say "in a nearby town" or "who work in a nearby town."

Last week 12 Vietnamese people came and we haved more than doubled the usual number of people in the class.

I notice this particular mistake a lot from non-native speakers; don't take this the wrong way. It is important to handle demonyms (住人の呼称) carefully in English. With demonyms ending in "-ese", using them the way you did sounds a bit offensive. Granted, it seems like this practice is gaining popularity online recently (I see it a lot on TikTok) but my opinion is that it is incorrect. A good rule of thumb is that if it ends in "-ese", add "person." There are situations where you don't have to (example, referring to an entire ethnic or national group: "The Chinese are known for their rich culture").

Apologies if this is complicated. Part of the reason I feel this way is because coincidentally, many countries with demonyms ending in -ese have a painful history of colonization by foreigners. Whether related or not, referring to people that way can evoke that negative history. Native speakers most likely would give you the benefit of the doubt, but I would definitely get weird looks if I did that around some of the people I know.