In the new version of Telegram 7.4, the transfer (export) of chats and messages from WhatsApp, Line and KakaoTalk became available for the first time.
Even if you are not in Telegram, you can still transfer the correspondence, but you will get access to it, so you should definitely take this into account.
The procedure for transferring chats and messages to Telegram from WhatsApp, Line and KakaoTalk is as follows:
1. Open WhatsApp, Line and KakaoTalk and find the desired chat
2. Swipe left on the selected chat and tap "More"
3. Select Export Chat
4. WhatsApp, Line and KakaoTalk will offer to export the chat with or without media files
5. After creating the archive with the chat, the Share window will appear, here you need to select Telegram
6. Select a group chat in Telegram into which you want to import the correspondence or create a new one
7. Wait for the message import process to finish
If you create a new group chat, you can then add other members.
Next to all messages transferred to Telegram, the Imported label and the transfer date will be displayed - this will be seen not only by you, but also by future participants in the recreated chat.