Wolfram Language File Encoding
Wolfram Notebook File Encoding
Wolfram Notebook is saved in pure 7-bits ASCII Characters. (even if it contains Unicode: Math Symbols ∑ ∫ π² ∞ or Unicode: Emoji 😄 ) [see Wolfram Language and Unicode]
This is just for your info. You don't don't have to do anything.
WolframScript File Encoding
WolframScript files accept any encoding.
I recommend saving WolframScript in "UTF8" format.