For your question, you can refer to this link for the different list of product codes with their respective regions.
RUT240 - 4G/LTE Wi-Fi Router | Teltonika Networks (teltonika-networks.com)
As you can see from that link RUT240X5XXXX region is Japan. So as an example the product code of the device based on the standard package will be like this RUT24005E000. You need to have this product code of RUT240 X5XXXX in order to work in Japanese bands.
If you have the exact LTE bands that the ISP is using it is much better :)
You can check the supported bands with matching frequencies in this link: RUT240 Supported Frequency Bands - Teltonika Networks Wiki (teltonika-networks.com)
I hope it helps