‘How would Langeron or Wilson know about Russian artillery training compared to other nations?’
By first-hand observation. Langeron was a Russian officer of long service. Wilson was with the Russian army as an observer for quite some time. And, yes, it is their opinion which is why it was posted. And the author who referred to Langeron’s opinion on the Russian artillery used mostly Russian references for his book.
’Most likley - they wouldn't and just expressed their opinion.’
You don’t know that unless you research the material. Do you have anything that suggests the contrary?
’This alone is not suitable to come to the conclusion to state that the Russian artillery officiers training was worse as in Britain.’
You are correct-it isn’t. That was why other material was used also that corroborated the first-hand observations of these two officers.
’One has to consult Russian sources.’
That is exactly what the authors of the book I quoted did. And that was why I used the material. So, Russian material was used and the opinions of these two officers was corroborated by it.