Some words don't only have a meaning, they are also emotive, and create a feeling in the listener or reader. To some people, the word "foreigner" sounds cold and distant, lacking any warmth or spark of friendship.  However, the adjective "foreign" does not connote a lack of warmth.  I therefore recommend you express your thought in a way which sounds "friendlier".  Here are some possibilities:

"To all our dear foreign friends"

"To all our dear friends from around the world"

About the Language Marathon!

Could you please check it. Is it to see whether it's correct or not? And By the way, if you are interested in participating, just ask me. ;)

Just remember that we phrase requests as questions. "Please check it" is understandable, but it sounds like a command. In some contexts this would be rude, so we make it a question to be polite. Also, avoid the "cool" abbreviations you see online. Your message looks far better when written in standard English. :)

To all our dear foreigners: I haven't forgotten about you! Thank you all guys for being patient and understanding. :)

I know the exclamation mark (!) is normal when addressing people in Russian, but it sounds excessive in English.

So, what's a Language Marathon? What is it?
It is a space when we learn languages together. Everything becomes easier and funnier when you have a company! I guess you meant "more comical" when you wrote funnier?

What's more, we have an 8-week schedule structure, based on 8 weeks. It which will help you to learn any language effectively, and in all aspects!

For the whole period (which is two months, remember?) you study by yourself. You create your own plan (under our control, of course:)) and do your best!

The parentheses and emoticon look a little messy. Can they be removed? 

Take note! For the right results, you need to study REGULARLY. At least, 4 days a week!
Also, you will be given a task each week (for everybody) and you have to do it which you must do. This applies to everybody.  

To participate in the marathon, you have to choose a language and to write it down in the comments (below). Also, tell us what your level is in this language.

On the 12th of October, we will start learning together! After writing down about telling us your chosen language, you have to wait for the instructions. :)

If you have any questions, please feel free to ask!

You are always welcome :) Not needed.

About language marathon!

Please check it. Is it correct or not? And btw! if you are interested in participating, ask me ;)

For our dear foreigners! I didn't forget about you! Thank you all guys for waiting and understanding :)

So Language marathon. What is it?
It is a space when we learn languages together! When you have a company, everything becomes easier and funnier!
Moreover, we have a structure, based on 8 weeks. It will help you to learn any language effective and in all aspects!

All the time (2 months, remember?) you study by yourself. You create your own plan (under our control, of course:)) and do your best!
Attention! For the result you have to study REGULARY. At least, 4 days a week!
Also you will have a task for week (for everybody) and you have to do it.

For participating in marathon you have to choose language and to write it down in comments (below). Also mention how your level is in this language.

We will start learning on the 12th of October together! After writing down about your chosen language you have to wait for the instructions :)

If you have any question, please feel free to ask!

You are always welcome :)