macbook changes writting language randomly

Hey people,

I have a weird problem and it seems I cannot figure it out.

I bought a new MacBook Pro M1 and set it up like the MacBook I had before that, but this one behaves a little differently.

The problem here is that when I type something the laptop keeps changing the writing language after a few symbols or actions (they are always the same ones).

For example when I write my email address, after the symbol @ it changes the language to Bulgarian.

When I write the word "iPhone" it changes the language after the "I" and it becomes like this - iПхоне.

Sometimes when I use the input source combination it doesn't change the language ( even if it is showing the new language) for 4-5 times.

Sometimes when filling a online form with different fields it changes the language on every different field.

I am struggling with that problem for 1 month already and it is driving me insane..... and my job is to write all day, so it is really a problem for me.

Looking forward hearing thoughts about that.