We recommand you to place your theme language files in child theme languages directory and also use the child theme.
If the parent theme gets updated (and most likely its language files too ...) your child theme translations keep untouched. 

Please visit the following links to learn more about translating WordPress themes:

http://codex.wordpress.org/WordPress_in_Your_Language
https://make.wordpress.org/docs/theme-developer-handbook/part-two-theme-functionality/localization/
http://codex.wordpress.org/Function_Reference/load_theme_textdomain