Marion,
Did the translator plugin work for you? It didn’t work right for me.
So I did this instead:
Go to Themes > Editor.
(Switch to ColorMag on the top-right if you are using a Child Theme… if you don’t know what that is then you’re not using one, it has to be set up manually, by you.)
Then click Content.php.
Then press Ctrl+F (to create a “find” box in your browser window. And search for “Read”.
Once you find something that looks like this: php _e( ‘Read more’, ‘colormag’ );
Switch the READ MORE to whatever text you want.
Then click Update File at the bottom of your window.
NOTE: This will have to be redone each time you update ColorMag. I just have a note in my website notes that says “READ MORE is located in Content.php” so that I remember where to find it.