How to change the TeXShop spell check dictionary to American English?

TeXShop is a popular LaTex editor for macOS. If the spell check goes to the British English, you may see something like this:

To change the dictionary, go to TeXShop -> Preferences.

Select Source -> Dictionary.

Select 'en' for American English. 

If it is already 'en', try select another option and quit TeXShop. Restart TeXShop again after you select 'en'. 

Final result:

Reference:

How to Change TeXShop dictionary to American English? (StackExchange) (The answers were a bit outdated.)