* 日本で (nihon de): This is the most common and general way to say "in Japan." It uses the particle で (de), which indicates location.
* 日本に (nihon ni): This translates to "in/to Japan," and is used when the verb implies movement *to* Japan or when the focus is on the destination. For example, "I went to Japan" would be 日本に行きました (Nihon ni ikimashita).
The best choice depends on the sentence. To help me give you the most accurate translation, please provide the full sentence you're trying to translate.