Do you know any Japanese? Peppering your work with local language, when done well, can add character, authenticity and ambiance to a novel and you don't have to tell the reader outright that the characters are speaking Japanese.
For example, Troppo by Madelaine Dickie won the T.A.G Hungerford award. It's set in Indonesia but written in English. Madelaine uses the local language beautifully and even though you don't always know what the words mean, the scene isn't lost. It's a gritty book with lots of swearing, so I've starred it out, but you get the idea.
On the bus to Sukadana I vomit for eight hours straight into
sandwich-sized plastic bags.
Halfway into the trip, I s*** myself.
“Oh f***. Tell the driver to stop,” I ask the conductor up the back.
“Sebentar, sebentar,” he waves his hand, palm-down, and lights another
He obviously hasn’t smelt it yet, but by the time we get to the rumah
makan (the roadside food house), his head is out the window and the
seats around me are empty.
We stop for half an hour. I spend the whole time in the toilets,
sobbing and sucking in the furry smell of old c***. I consider leaving
the bus but there are no rooms at the rumah makan and no village
nearby, only the hazy midday stretch of rice fields and pandanas
This scene is at the start of the novel and from that point forward, she doesn't need to tell you that a kretek is a cigarette or that a rumah makan is a roadside foodhouse. You might not know that sebentar means 'in a minute' but you get the gist.
Reading the book, you feel like you're in Indo. Language can be a really effective tool for adding authenticity.