Found the solution!
If anyone wants to do something like this, i share it:

in localizedstrings/cgame.str (for ex.)

add the following lines:

REFERENCE SB_KILLS <--this is the scoreboard line ( there are more: SB_DEATHS, SB_ASSISTS etc...)
LANG_ENGLISH "Text what scoreboard write instead of kills"

Hope i could help!
Have a nice day!