Add multi-language support to the start screen and help-modal

[Aotumuri]

This pull request adds multi-language support to the start screen.
Languages are managed via JSON files, making it easy to add new languages in the future.

I added a basic language selection button for switching between languages.
However, I believe it would benefit from a better design — my design skills are limited, so I apologize in advance.

Looking forward to your feedback and possible design improvements.

[Aotumuri]

This screenshot shows how the interface behaves when the language is set to Japanese.

This screenshot makes it clear that the language switch button needs visual improvement.
I’m not confident in my ability to improve this button’s design, so any suggestions would be greatly appreciated!

[Aotumuri]

Here’s the current progress on the multilingual support work.
I’d appreciate it if you could let me know whether it’s okay to move forward with it as is.

• start screen (en -> ja)
• help-modal (en -> ja)
• Join game
• single-player-modal
• host-lobby-modal
• game
  etc.

If anyone is willing to help with translations into languages other than Japanese, it would be greatly appreciated!

[Aotumuri]

As I mentioned on Discord, I’d like to leave a note here as well.
The goal of this pull request is to implement a system that allows easy application of translations—not to translate all the text right now.
Ideally, I’d love to help translate the game and make it more accessible to a wider audience.
That’s why I believe even partial translations (even if not everything is fully localized) are still meaningful and valuable at this stage.

[evanpelle]

thanks!