> you can usually just drop foreign words directly into English without any special twists. It seems much more fiddly in French, German, etc. In Japanese you always have to modify the pronunciation of English words
I dunno what you mean by "have to" here, but English, like most languages, has both a limited set of phonemes and unique patterns of how they are combined and how stress is distributed, and, like most languages, loanwords will usually have their pronunciation changed to fit that phoneme inventory and construction patterns.
English, because any phonetic interpretation of its spelling is more what you'd call guidelines (or may be just jokes) than actual rules is probably less likely to change the spelling of loan words from other languages that use the same alphabet or one with a well-established transliteration, but the actual pronunciation is a different story.