When translating not all string are present in POedit

PO/MO files’ content depends on the theme/plugin developer. So you bought a half-ready theme… One way is translate strings in php files, but with this you loose the chance to update that, because updates will overwrite your changes.

I suggest you: translate the strings with po/mo, than send the updated files to the developer too, so maybe the next theme’s version will contain your languages and changes too.

To translate string, use __('[STRING]', '[TEXTDOMAIN]'), for example you see a “Sidebar” string, then change that in php something similar: <?php __('Sidebar', 'mythemetextdomain'); ?>, than add to po:

msgid "Sidebar"
msgstr "SlovakianSidebarName"

Your theme’s text domain maybe in the style.css header.