[feature]: support multilingual search setting

[xrafece]

Can the developer add a preference for language settings? Sometimes, I need to replace the language in the search url with something other than English.

I think just change SearchIndexURL to a setting map.

file -> manifest-v3/background.js

const SearchIndexURL = 'https://developer.mozilla.org/en-US/search-index.json';

Finally, thanks to the developers for review this Issue!

[hanguokai]

Technically, this extension can support more languages.

Here are some blogs about MDN localization strategies:

• 2021.03 MDN localization in March — Tier 1 locales unfrozen, and future plans
• 2021.02 MDN localization update, February 2021
• 2020.12 An update on MDN Web Docs’ localization strategy

As you can see, MDN itself has some issues with localization support.

I'll try to add options for Tier 1 languages when I have time.

[xrafece]

I get it! Thanks for your reply！