I'm not an expert, Bear, but this is my experience... Certain letters/sounds are hard to pronounce because a person's native language doesn't use that part of the mouth to make that language sound (e.g. Chinese may not produce that "R" sound in many words). Sounds come from many places:
* Throat
* Back of mouth
* Tongue on roof of mouth
* Tongue behind front teeth
* Tongue between top and bottom teeth
* Lips
Think about Chinese and how you make tones. Your mouth/throat produces each tone a little different. Each Chinese letter comes from a different place in the mouth, too.
With the Spanish/Swedish "R", your mind and mouth probably don't have the skill of creating that sound. If you find out WHERE in the mouth/throat a sounds comes from (like "R"), anyone can probably begin to produce it.
Native speakers who also teach that language can explain where the sound comes from, and what your tongue or throat should feel when producing that sound, I think any sound can be taught to anybody. Excellent teachers will be able to describe the feeling you should have. A fluent Chinese speaker who also speaks Spanish or Swedish will even be able to give you Chinese words that come close to reproducing that "R" sound.