(Web Platform & Andriod App) - Design Chat Platform Similar to Whatsapp

I am interested in making a private chat platform similar to whatsapp. The platform will have as a minimum all functions and features available in whatsapp. However, we have a different model and more functions to be developed. The platform needs to be developed in English and Arabic. The platform will be used in our company, the intention is not to make it public.

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Please respond ONLY if you ave done similar projects in the past. All responses without experience info, will be ignored.

Thanks.