Add Spanish (es) language support

[sebas-tcotd]

Hi! I noticed the app already includes an internal i18n system (ja, en, zh).

I’d like to contribute Spanish (es) language support by:

• Adding translations for the existing keys in i18n.js
• Integrating Spanish into the language selector
• Adding the corresponding flag asset

This should expand accessibility for Spanish-speaking users without changing the current architecture.

Would you be open to this contribution? I’d be happy to open a PR.

[iamcheyan]

Thanks, that sounds great. Feel free to go ahead and open a PR.
Please make sure the translations follow the existing structure in i18n.js.