Japanese doesn't have an actual language group like most languages do (e.g. Danish is part of the North Germanic language group, closely related to Swedish and Norwegian), however, I have heard that Korean would be the most closely related, as both languages borrowed common characters from the chinese language and also my guess would be they are reasonably similar given they are geographically close, however, by no means mutually intelligible.
Yes, the Pomeranian breed is closely related to the Japanese Spitz.
Korea is more closely related to Chinese culture than Japanese culture. This is because Korea has a long history of cultural exchange and influence with China, including language, religion, and customs.
The language most closely related to English is Frisian, a language spoken in the Netherlands and Germany.
English is most closely related to the Germanic language family, specifically the West Germanic branch.
Persian
Japanese Americans were most closely related to the War Relocation Centers.
It's most closely related to Estonian.Estonian, and Saami (Lapp)estonian
the tribal languages of central and southeastern siberia
The language most closely related to Vietnamese is Muong, which is a language spoken by the Muong ethnic group in Vietnam. Both Vietnamese and Muong belong to the Vietic branch of the Austroasiatic language family.
The relationship between Japanese and Korean has been debated. Some claim that Japanese and Korean are both considered Altaic, along with other languages such as Turkish. Others claim that Japanese and Koreans are more closely related. Currently, Korean is believed to be a language isolate (and if this is true, it is the most used language isolate in the world) and Japanese belongs to the Japonic family, of which its classification remains unknown.
Maybe Estonian
Zero. Japanese is not related to any other language. There is a common misconception that Japanese is related to Chinese, but this is untrue. Japanese has borrowed many words and some of the writing system from Chinese, but the two language families are completely unrelated.