Learning English, especially the pronunciation
I've been learning English since I was 13, at a junior high school. My mother works as an interpreter, so while I didn't follow her career, I've always been familiar with English with some periods of breaks on and off. I needed to talk in English from time to time at my work, and I had never imagined of learning another language besides English.
So living in France was something I had never expected, nor is learning French. English and French are similar to some extent (compared to Japanese, of course) in terms of grammar, but their pronunciations differ a lot. After having spent a certain time studying French, I noticed one thing: now I feel more tired in speaking English.
If you see facial expressions of Japanese people, it wouldn't take long to understand that we don't move our mouth as much as the Americans, just because that's how our language is spoken. The intonation is much weaker, and the type of pronunciation has a less variety. In addition, we are not inclined to show our emotion in the way Amercains usually do, consisting one of the biggest cultural differences between two countries.
However, though I have to admet that my French pronunciation is nowhere near perfect, the French language, the French language requires not much of the motion of mouth in comparison with English. With the intonation much flatter (though throughout the sentence there is a intonation), I was more at ease while learning to converse in French, which made me realize that English demands some muscles that I don't use for Japanese and French.
That being said, in Japan (and I guess in most of the Asian countries), we adopt American English education, so it goes without saying that the pronunciation takes the American style. On the contrary, my sister learned English at New Zealand, and she affirms that New Zealand English or British English is less complicated in pronouncing. Getting used to speaking with other English accents might help me get through this muscle problem, but it would not be easy to relearn the accent from the scratch.