joru

Found a third date format string
content-single.php, line 52
new:
<?php the_modified_date( __('F j, Y', 'celestial'), __( '<span class="modified-date">Last Modified: </span> ', 'celestial') ); ?>
Maybe there are some more

There is also an error in the language file. In functions.php, line 576, you use the function
_x( 'Comment', 'noun', 'celestial' )
But the correspondent
msgctxt "noun"
in the language file is missing. Should be inserted after line 286 in celestial.pot. So that it looks like

#: functions.php:573
msgctxt "noun"
msgid "Comment"
msgstr ""

Not sure if you use _x() somewhere else.

Hope that helps.