Open your config.cfg file (which should be in your personnal game directory, as "counter-strike/cstrike" or "counter-strike/cstrike_polish" (if you have cs in your language) then add this line to the end of the file (just after the setinfo list).
setinfo "_lang" "pl"
Save your file then go to play CS on CSCREAM...
If this solution fix the problem, that means your config.cfg file was probably in readonly mode (can't be modified in game), or maybe your setinfo limit was reached.