Add translations for `proposals.community_translations`

[smorimoto]

Translation status of each language

At the time this issue was created, work has already been completed in French and Russian, but not yet in the other languages. Anyone interested in working on this, raise your hand on this issue. (To prevent duplication of effort among multiple contributors!)

Language	Status	Link
German Translation	🚧	tc39.github.io/de/proposals.json Line 29 in be8c92e "community_translations": "This page is translated by the community. If you want to contribute, read our <a href=\"https://github.com/tc39/tc39.github.io/blob/main/translation_de.md\">guidelines</a>.",
French Translation	✅	tc39.github.io/fr/proposals.json Line 29 in be8c92e "community_translations": "Cette page est traduite par la communauté. Si vous souhaitez contribuer, lisez nos <a href=\"https://github.com/tc39/tc39.github.io/blob/main/translation.md\">directives</a>.",
Japanese Translation	✅	tc39.github.io/ja/proposals.json Line 29 in be8c92e "community_translations": "このページはコミュニティによって翻訳されています。貢献したい場合は、<a href=\"https://github.com/tc39/tc39.github.io/blob/main/translation_ja.md\">ガイドライン</a>をお読みください。",
Russian Translation	✅	tc39.github.io/ru/proposals.json Line 29 in be8c92e "community_translations": "Эта страница переведена сообществом. Если Вы хотите сделать вклад, прочитайте наши <a href=\"https://github.com/tc39/tc39.github.io/blob/main/translation_ru.md\">гайдлайны</a>.",
Simplified Chinese	✅	tc39.github.io/zh-Hans/proposals.json Line 29 in be8c92e "community_translations": "这个页面的翻译是由社区贡献的。如果你也想贡献，请阅读我们的<a href=\"https://github.com/tc39/tc39.github.io/blob/main/translation_zh-Hans.md\">指引</a>。",

[Ritish134]

Hi there would like to work on this issue can you assign it to me