proving that the set of all english words is countble. This is the question :
Prove that the set of all the words in the English language is countble (the set's cardinality is אo)
A word is defined as a finite sequence of letters in the English language.
I'm not really sure how to start this. I know that a finite union of countble sets is countble and i think this is the way to start.
Thanks in advance !

There are $26$ letters in the English language.
Consider each letter as one of the digits on base $27$:


*

*$A=1$

*$B=2$

*$C=3$

*$\dots$

*$Z=26$


Then map each word to the corresponding integer on base $27$, for example:
$\text{BAGDAD}=217414_{27}=2\cdot27^5+1\cdot27^4+7\cdot27^3+4\cdot27^2+1\cdot27^1+4\cdot27^0$.
This mapping yields that the cardinality of your set is $\leq|\mathbb{N}|$, hence this set is countable.
