Based on my own experience, Japanese isn't a highly difficult language to learn so mastering it is definitely possible, but it does require determination and patience. Substantial progress can be made within a rather short period of time. For example, in less than a week, I became capable of:
- counting up to 100
- listing the days of the week
- correctly expressing days of the month
- recognising tenses
- distinguishing between positive/negative
- understanding and using basic expressions/constructing basic sentences
Sadly, I haven't been able to progress past this point due to the lack of time, but I am still familiar with most of the above.
Chinese is definitely more difficult and takes more time to master than Japanese. It's definitely great to see people (such as the person in the video below) speak Chinese at a very high level. Perhaps wzsmartypants (being a native Chinese speaker) may have comments about it: