Yes, it's the point of "basic knowledge", and thus it applies to all/most "languages". So, once you have learnt the "basic" of simplified Chinese, it's just a piece of cake for further guessing.
For the priority, there is not a must for everyone. If time for learning a new language (or any other kind of new knowledge) is limited, depends on one's daily use and need and how urgent the situation is, one can set his/her own schedule in order to fulfill his/her need/interest.
But generally speaking, if you are living in HK/Van, you can't go wrong to learn all the following three languages: Cantonese, English, and Mandarin for speaking (by alphabetical order, not the importance); and English, Simplified Chinese, and Traditional Chinese for written. |