Their English will probably improve over time, especially since it's unlikely any other residents of the town speak Japanese.
Today I went to the pharmacy at RiteAid. They had a new assistant. A pleasant young Asian woman. When she hesitated while punching in my birthdate, she said, "I can never remember which months have only 30 days; I'm sorry."
I told her there was a rhyme for that, and did the "Thirty days has September, April, June, and November" thing. She looked confused, and really, I can't say I blamed her. She told me, "In China, we do this..." and did a thing sort of counting on her knuckles.
Obviously, neither language has a really adequate way of explaining it. So we both laughed. But her English was excellent. Accented and not perfect, but very good. I wonder if she's a student who has a part time job to make ends meet.