I realized that I can have problems with single quotes in php arrays:
<?php
$lang = array(
'tagline' => 'Let's start your project',
"h1" => "About Me"
);
?>
So I changed it to double quotes:
<?php
$lang = array(
"tagline" => "Let's start your project",
"h1" => "About Me"
);
?>
Should I use "php quote escapes", instead of what I just did? (by the way how to write "php quote escapes"?)