That`s what i mean:
Starting from the fact that when you state that the server is really international and as such English language should be the prevalent language used to comunicate to the rest of the community (trade chat&party matching), of course this can't always be carried out as some of the Russian players do not know English, in this case they could use simple tags (WTS/WTT/LF and so on) in order to let everyone know what they are searching for.
Furthermore what i have noticed is that even the ones who have learned English still prefer to use Russian titles, causing problems to the "foreign players".
Lastly as you said the currently international community is not more than 20% (and might increase to up 25%) of the total players which means around 3500 players out of 15.000 total online, so i guess it is worth a try to really make it international and make it comfortable for everyone.