Chinese and Arabic are the toughest I have found. Its a nightmare. In Chinese Mandarin is easier than Cantonese though, there are less way you can say the same word in Mandarin, hence fewer meanings.😆. 4 for Mandarin as opposed to 9 I think for Cantonese. Like I said, a nightmare.
Between the two you mentioned I would say Japanese. You have to go a really long way before you can write anything of value in Japanese. Way too many words to learn.
Also in the end it comes down to the person's interest as well. If you are really interested you will find it much, much easier than the average person.
Regarding as to whether they will learn the whole language, nope; they won't. I doubt they will go beyond their dialogues, even to the basics of grammar, vocabulary etc. I don't think Bollywood is really there yet to get that amount of detail right; though this is an encouraging trends.
The most important thing they need to work on most is the accents. Its harsh to expect them to take full language courses. But yeah basic garment, vocabulary should be studied imo. It makes the performances that much better, if you understand what you are doing and the room for improvisation increases.
If you know urdu...then it's very very easy to learn Arabic
Anupamaa
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