WordPress Translation Issue

I tried to change text using the below code

function ctxtlearn_gettext( $ctxttranslation, $ctxttext ) {
   $ctxttrans = array_values(changeTxt_setting('trans',true));
   $ctxtdirty = false;
   $ctxtstrings_map = array();
   $ctxttext_words = explode( ' ', $ctxttext );

   foreach($ctxttrans  as $ctxtmytrans) {
	   $ctxtstrings_map[$ctxtmytrans['key']] = $ctxtmytrans['val'];
   }

   foreach ( $ctxttext_words as $ctxtk => $ctxtword ) {
	   $ctxtw = trim( $ctxtword, '.,:!?-_()' );
	   if ( isset( $ctxtstrings_map[ $ctxtw ] ) ) {

		   $ctxttext_words[ $ctxtk ] = str_replace( $ctxtw, $ctxtstrings_map[ $ctxtw ], $ctxtword );
		   $ctxtdirty = true;
	   }
   }

   if ( $ctxtdirty ) {
	   return implode( ' ', $ctxttext_words );
   }
   return $ctxttranslation;
}
add_filter( 'gettext', 'ctxtlearn_gettext', 10, 2 );

If i give the below input it works

Post => My Book
Page => My Vertical
Comments => My Feedback

The Word before => is old string and after that is new string. if i pass it as an array it work’s. but if i provide the below input

First Name => My Name
Username => User ID

The username text changes but First Name Not Changing in profile page.
But if i split and provide its getting changed.

Who i can do this by providing Whole String..?