First, a little of my background, I have been living in Australia
for almost 7 years. And I will turn 22 in a few months. Some of the
following will have some scientific practicality, but most will be
anecdotal, from my own experiences.
Before learning a language, you have to ask yourself: Why do I want
to learn this language? I may not even need this skill to live my
life. It is essential that you find your motive before continuing.
For example, "I want to learn English so when COVID is gone, I can
travel to the US." So, you want to go to the US, experience the life
in this foreign country, and the prerequisite to enjoyable, memorable
and fun experiences is having a descent speaking skill.
Some people may learn a language for different purposes, for example,
many priests in Vatican city learn Latin, but they do not converse in
Latin, the language is mainly used for ceremonial purposes. Some of
my friends only learn a bit of English so they can understand the
textbooks for their study, not something they use for verbal
communication.
The reason you want to find your motive is that the vocabulary varies
in different context, like normal people would never speak like
Othello by Shakespeare. Here I want to introduce a scientic phenomenon
called Zipf's Law. It is an observation of the mathematical
relationship between each words. Let's use English as an example, the
word "the" is the most common word in English followed by "of" "and"
"a", and the frequency of the word "of" occurs is half to "the", "and"
is one third to "the", "a" is a quarter and so on. You may ask: Why
does this have to do with learning a language? If you understand the
principle behind it, this is actaully applicable to every aspect in
life. I am yet again going to introduce another peculiar phenomenon,
Pareto distribution, which states that 20% of the causes account for
80% of the outcomes, or simply 80-20 law. In the context of English,
only 20% of English words are involved in 80% of the conversations.
So, how many words are there in English, and how many for 20%? There
is no clear answer to that, but I would say, if you know 1000 common
words, you are quite descent already, and that would probably
suffice for your travel.
To recap briefly, depending on your purpose for learning a particular
language, the complexity of the vocabulary that you will be using
will be different, and you should accommodate yourself so that you
are learning the things you need, although it does not hurt if you
can learn more than that.
I will continue some time this week!