How many words do you want to learn when you want to „master it well“? Let’s say you mean 100,000 words. How many hours in one year? Let’s say 1,750 hours. This means you have only about one minute of learning time per word on average. That’s not much.
In addition, there’s some grammar to master.
If you are such a language learning genius like Daniel Tammet, you will need much less than one year. He learned conversational Icelandic and conversational German within one week.