Swedish - many words are the same and so is the grammar. When the Vikings settled in England, they influenced the language.
German is also easy, thought the grammar is different. English and German were rooted in the same language about 1000 years ago. That changed when the French invaded in 1066.
Chinese has been hard for me because the grammar is different, there are no common words, getting the tones right is difficult and there is no phonetic alphabet.
Korean was a bit easier because it has a phonetic alphabet. I've forgotten most of my Korean, but I can still sound out words because I remember their alphabet. (I just don't know the meaning.)