Subtitles in BF4 campaign - Can I make my own?

As the title says, I would like to make my own subtitle in campaign. I was thinking something like Serbian/Croatian/Bosnian translation of the English subtitle. And I would like to ask, which program I need to use to make subtitle or it is impossible to make one? Here is the link from the forum >> http://battlelog.battlefield.com/bf4/forum/threadview/2979150493842980983/


Best regards, 

Nikoladiv