In Japan there are some food products that are identical to American brands but with Japanese packaging. For example, here is the Japanese box for Ritz crackers:
Ritz are certified kosher in America (OU-D). Does this apply to the Japanese Ritz as well? They might be manufactured in the same plant and simply repackaged, but perhaps Nabisco also manufactures separately in Japan.
Outside of Israel and the US, observant Jews don't rely on Hecshers to buy food, because as you've noticed from the Japanese box, there just aren't any hecshers. Rabbis in these communities give out lists of acceptable ingredients (or lists of non acceptable ingredients) and people go and shop at their local markets and buy unsupervised food all the time.
If the ingredients are the same as hecshered products, then it's kasher as well. You can visit the Kashrut.org website ran by the renown poseq Rabbi Yiztchak Abadi where he states what is or isn't kasher based on ingredients. His ingredients only ruling is based on the Gemera, Shulchan Aruch, and a Teshuvah by Rav Moshe Feinstein.
If you search the forums you can find designations for what things that are inherently kasher and what things are problematic so that you can navigate ingredients yourself without having to ask. Here is a search on Kashrut.org regarding crackers.
So in short, if the ingredients of your Japanese Ritz crackers are the same as their American parts then they are Kasher.
