The main cause of incompatibilities with Gengo is this line:
If you see this line near the top of the plugin file, that is probably the reason the plugin won’t work with Gengo. Just like the code that adds widget-capabilities to plugins, calls to load_plugin_textdomain cannot be made immediately. Plugins must call load_plugin_textdomain inside a function that runs on the ‘init’ hook, or at the earliest, the ‘plugins_loaded’ hook. Plugins that do not do this are coded incorrectly, according to advice from WordPress core developers. The fix for this is usually simply a matter of moving that single line of code to the correct place. If you find this problem affecting a plugin you are using, do your plugin author a favour and let them know (politely). Gengo will not change to accommodate broken plugins.