Using messaging systems such as Telegram to improve our English
It would highly appreciated if you could share your experiences with me about this subject. What are the pros and cons of them? Is it safe?

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I haven't heard of it either.
If it is a messaging system, surely the most important part is who you talk to, rather than the system itself. I guess that that leads onto the question of how popular a given messaging system is among native speakers of the language you want to learn.
Hopefully this question is not just spam!

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Hi Camilo! Telegram is a Russian instant messaging systems, it's very similar to WhatsApp and Viber. These days, Telegram is the most popular with my countrymen. :)

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I have never heard of Telegram.