1) I think Chinese would be a huge advantage, especially since there is a large segment of the population that speaks it all of the time. The reason for this is because many chinese companies do business mostly with each other------in chinese.
2) Even as a foreigner (arab) its important because language is both a unifying factor between people but also separates you from other non-speakers. Who will a chinese hire, the one who speaks chinese or the one who doesnt? If they could hire you and you could talk on the phone to a client in China or Taiwan, is that an advantage to the company or not? I know many chinese in business who do not speak any english at all. Just today I called a bike workshop to see if they were opened on the holiday and the chinese lady who answered couldnt speak one word of english.
3) China is expanding all over the planet and in the future knowing mandarin will be as important as english.
4) Thats also the problem, which chinese dialect to learn? Mandarin? Cantonese? Hokkien? Hokka? Which one? I would choose mandarin since its the language of Beijing.
5) You say you forget with non-use. In Malaysia you can use it 24/7. Is that enough?
6) Its extremely hard for an adult to learn it. The older, the longer. The average is 7-10 years, I read somewhere. As a young person it would be far easier, especially for children. I have tried to learn and I cant do it. I taught myself to read and write about 200 characters but im unable to speak it or even remember it. Same with vietnamese.
7) Last I can think of for now is that another reason to learn it fast is because it functions as a secret code in the country. Its how chinese keep secrets from the other races because very few non-chinese speak it. Even in a business meeting chinese will talk to each other behind your back about you and you sit there like an idiot, not knowing they may be putting a knife in your back. Also, many signboards around the country are messages to other chinese. Chinese in Malaysia almost functions as a parallel country.
8) Oh.....last thing is HOW to learn it? Yes...when...where....who teaches? This is a problem which cannot be answered by simply saying "try YMCA." You may have to purchase expensive online courses. I once tried to enroll in a childrens school so that I could learn it the same way children do but they refused me. There are sometimes private tutors around KL who offer classes for RM80 per hour and you may have to do that. Three or four hours a week, about RM1200 per month. Thats like a car or house payment! Years of that and you will know chinese and also be in bankruptcy too.