Localization: Add Japanese Translation

[ToshihiroMakuuchi]

This is a sudden pull request, but I wanted to enable Japanese localization, so I created the dictionary file messages.json.
Additionally, I have added Japanese as a selectable option alongside en and uk.

In the current version (8.0.0 RC1), it seems that Demo mode is not working properly. However, in version 7.1.2, the Japanese localization appears to be functioning as expected.

One issue is that the font for Japanese differs from the one used in Betaflight Configurator, making the appearance less readable. I am unsure where to modify the code to match the font with Betaflight Configurator. If you know how to adjust this, I would appreciate your guidance.

Thank you!

[b14ckyy]

Thanks a lot for that. I can't give you any info regarding the font unfortunately. Maybe a developer can answer that. Afaik its hard coded and can't be switched based on the localization right now.

It might take a bit until a localization is added as it needs to be translated back and doublecheck by someone else before we can merge it. Appreciate your work.

[ToshihiroMakuuchi]

@b14ckyy

Thank you for your previous response and the guidance regarding localization.

I have created a Japanese version of the messages.json file based on the latest version as of November 24th. I carefully reviewed all keys to ensure consistency with the English version and made adjustments where necessary. Additionally, I have revisited the translations to ensure that they are accurate and natural in Japanese.

I understand that the localization will need to be reviewed and double-checked before it can be added. If there are any further steps required, such as addressing specific localization concerns or providing additional context, please let me know. I am happy to assist in any way I can.

It is an honor to contribute to this project. I look forward to receiving feedback from the team.