Please who know how add new emojis?

No chance in getting the actual flag emoji changed, but Apple did support the addition of the rainbow flag emoji via an emoji ZWJ sequence in iOS 10.0

Emoji ZWJ sequence are quicker to implement because Vendors don't have to get approval from the unicode consortium for them.

Apple could add a emoji ZWJ sequence to produce the white-red-white flag in iOS 12, but It would take a lot of public pressure to make them do so.

National Flag emojis are handled by the Unicode Consortium, they take years to make changes and as Niel said, they will only update when the "internationally recognised government" of the country tells them its flag has changed.

The current Belarussian flag is already an emoji. Unless the government changes it, no others will be added.

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