Add new language

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This is a request to add sinhala language to below home assistants projects.

Language: Sinhala
Code: si

Projects: https://developers.home-assistant.io/docs/translations

• Frontend
• Backend
• iOS
• Android

Furthermore, i contribute as a translator / proofreader for eg: lineageos, joomla etc projects.
Email: [email protected] | Name: HelaBasa

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See also home-assistant/frontend#9832 (comment)