My question was rhetorical. The point is that the English word for "kefir" is "kefir". So English does have a word for that.
shkkmo stated the situation well and nothing you wrote in response refuted anything they said. You say "Just because a word is "in the dictionary" doesn't make it English" but that's not true, as they explained. Virtually the entirety of the English language is "loaned" from somewhere. From the Merriam-Webster definition of schadenfreude: "In English, the word was used mostly by academics until the early 1990s, when it was introduced to more general audiences via pop culture."
You say "that doesn't make it suddenly become English" -- indeed, it wasn't sudden. The word did not always appear in English language dictionaries. It was added when it became recognized as having been incorporated into English--lexicographers are conservative and lag behind actual usage.
Anyway, I'm not going to recreate the entire prescriptive/descriptive debate in linguistics here, especially since "kefir" and "schadenfreude" are English words on both grounds. Enough said.
