How to rewrite system language in themes

I want to redefine the language in the following php file in my theme, I have try to put the changed file in the theme dir, but it does not work . so is anyone know how to do this ?

question2answer-1.8.5qa-themeOstackBloglangen

qa-lang-emails.php

qa-lang-misc.php

qa-lang-main.php 
qa-lang-admin.php

qa-lang-options.php

qa-lang-profile.php

qa-lang-question.php

qa-lang-users.php