Is the Japanese "r" close enough to Esperanto's "r"?
I couldnt roll my r's if my life depended on it... But I think the Japanese R is pretty close to it, would I be understood pronouncing it like that?
For what it's worth: I studied French for 7 years at school, German for two, a smidgeon of Spanish, and had given up on ever being able to roll, trill, or do anything with my R. Then at the age of 19 I started Russian and suddenly it clicked and I've been able to do it ever since. My R is not "correct" in, say, French, but it's understood just fine.
Never having been able to roll an R =/= physically unable to do so.
I don't remember the Japanese R well enough to compare - isn't it quite soft/close to L? - but it's my understanding that Esperanto is relatively forgiving of poor accent, partly because very few people are native speakers and thus almost everyone has some kind of accent (even those growing up as native speakers tend to pick up the accents of their (usually non native) parents).
My understanding is that Esperanto R should be trilled (but doesn't have to be; any European R ought to be acceptable, I think). On the contrary, I've never heard a Japanese person pronounce a trilled R. The standard Japanese R is pretty much the same as the Spanish R (but not the trilled "rr!"), which is a flap very close to the "tt" in American "butter," although I've heard many people pronounce it as pretty much an English L. I believe this is a regional difference.
Trilled R can be difficult but is easier when you know where to put your tongue. In French, you must position it so that the area near the "root" is touching your uvula. Then you vibrate your tongue, and it vibrates your uvula. In Russian, it's easier: you curl your tongue upwards towards the back of the ridge at the front of your palate, and then vibrate the tip of your tongue. I believe the Spanish "rr" is slightly more forward, but I'm not sure. I'm not certain which of those two (if they are even different) is used in Esperanto.
That is harder to explain, but it's done with airflow, not the muscles of your tongue. If you position your tongue correctly, and you blow air out in the right way, you'll get it. It took me ages to get it, but now I've done it once, it's easy to do as many times as I want, even if I haven't quite got it to sound right in all possible syllables. The French one is harder and I can't do it consistently.