Translation files include only strings that were used in PHP files and can’t be edited from the Theme Options or backend. Search placeholder text of the header builder element is custom text and it can be changed via Theme Options > Header builder > Search, it’s not included to translation files because it’s not hardcoded. If you create multilanguage site using WPML for example then all the strings from the admin module could be added to the translation using WPML settings http://prntscr.com/qxsbgb to translate them to other languages.
What plugin do you plan to use to create multilanguage site? WPML?
