Well I know that I have been in Russian 10v10's and all the text appears in Russian, so I don't know if source games have any kind of ability to translate text..which would be ideal in this situation. I think that non-english speaking players are a big source of situations like this. The only somewhat easy way to help that I can think of is an animated spray that would cycle through commands in 2/3 languages.
We also have to consider what the average 10v10 server and player is like. There's maybe one other 10v10 that I have played in where people actually use mics. Most of them are full of silent players who just rush, leave their team behind and take advantage of the overpowered perks to massacre everything they come across. New players may find what goes on in the gc server to be surprising, unusual and may have never been in a 10v10 where people are actually trying to work together to win. Those of us who have 200+ hours logged on the server are playing from a much different perspective than a lot of the 10v10 community is. Sometimes I feel bad for new players, they get yelled at and ragged on constantly because they are lagging behind or going down the wrong path etc. I definitely get it, its annoying when you are moving along smoothly and a new guy drops in, gets incapped because he's shopping alone in the back. But "DON'T SHOP!!!!!!" and "Hey _____, shopping is a bad idea on this server because...." can produce two drastically different reactions from the offending player. I think just politely letting people know what the server is about would go along way...not that their aren't helpful or polite people around here because there definitely are, but I also see a lot of overreacting to new players mistakes.