No, NiMH batteries will vary by capacity. I’ve seen rated capacities as low as 1600mah (and heard of lower) and as high as 2200mah. The actual capacity can vary some from stated capcity but there can be a huge difference between brands.
Not all chargers work the same. Some fast chargers will heat the cells a lot and this can damage them and dramatically shorten life. Some of the early Rayovac chargers were prone to this and I’ve had cells get so hot the plastic coating actually melts and splits. I now use a Lenmar Gama charger which is fast but keeps the cells cool.
I’m not sure what utility voltage is in Japan but I know it’s 220 in Europe. If your charger has a conventional transformer power supply it probably can’t work on different line voltage than it was designed for. Switching power supplies which are very light and compact are becoming more common and they can accomodate dfferent supply voltage. Check the actual specifications on the power supply.