Enable filtering with multiple languages and spoken-languages

[fgsepter]

Checklist

• [x] My code is properly formatted using the latest black
• [x] I have added/updated tests if needed
• [x] I have tried running my code manually
• [x] I have checked for spelling errors

Description

I have made changes to enable filtering with multiple languages and spoken languages. We can search based on various combinations of languages and spoken languages. For example, we can use -l Python+JavaScript to filter two languages Python and JavaScript, and -S zh+en to filter Chinese and English.

[hedyhli]

Closing this PR as it's stale. If you have other improvements to the code, feel free to open another PR :)