Hi Natasha, this was a very interesting question! As it turns out, some speech impediments are related to brain activity. Let me explain with one example of a speech impediment you may come across with native English speakers - stuttering. It's been documented that a stutter is related to the Broca's area of our brain, the part that helps us develop the sounds of speech. So it is reasonable to conclude that if the Broca's area isn't functioning properly or receiving enough blood flow this will affect speech, regardless of the language. Perhaps sign languages are the only languages not affected by speech impediments. You may find this short video on stuttering interesting. I hope this helps! https://www.youtube.com/watch?v=Wj8gz0Rp_GY

Interesting question. I've never thought of this before. I have no knowledge about speech impediments but I would be very surprised if a person had trouble speaking one language and no troubles speaking another language.

Russian people may have problems pronouncing hard 'r' very softly, 'sh' and 'sch' as kind of 'ths', 's' as 'f' and 'l' as kind of 'v'. Children and some adults who have such speech impediment usually visit speech therapist to learn proper pronunciation.