• includes/class-mysql.php
  "YOURLS requires the mysql, mysqli or pdo_mysql PHP extension"
  ->
  "YOURLS requires at least one of these PHP extensions: %s", "<code>mysql, mysqli, pdo_mysql</code>"
• admin/tools.php#103
  remove trailing space

(Make this change late in the 1.8 dev cycle: if there is no new other translatable string, postpone to 2.0)