Important WordPress plugins for programmers:
P3 (Plugin Performance Profiler) – See which plugins are slowing down your site. This plugin creates a performance report for your site.
WP safe updates – Test WordPress plugin updates safely before applying them on the live site. Create sandbox where the user can safely test updating plugins without affecting the live site.
General Important WordPress plugins:
Wordfence – one of the best security plugin / toolset for WP, include website firewall.
Sucuri Security – Auditing, Malware Scanner and Security Hardening. Another security plugin / toolset for WP.
Ceceppa Multilingua – Simple & free multi-language plugin for WP.
Accessible Poetry – Add basic accessibility options in your website.