I have same issue and tried to reinstall/install many times even with Sketchucation plugin maneger but none of the fredo's plugins work for me, and this is the error on Ruby console:
Error: #<NameError: uninitialized constant Traductor::Plugin::G6B>
/users/asadullahshafai/library/application support/sketchup 2019/sketchup/plugins/fredo6_!libfredo6/lib6plugin.rbe:1868:in tem_context' /users/asadullahshafai/library/application support/sketchup 2019/sketchup/plugins/fredo6_!libfredo6/lib6plugin.rbe:1656:in tem_launcher'
/users/asadullahshafai/library/application support/sketchup 2019/sketchup/plugins/fredo6_!libfredo6/lib6plugin.rbe:119:in launch_action' /users/asadullahshafai/library/application support/sketchup 2019/sketchup/plugins/fredo6_!libfredo6/lib6plugin.rbe:244:in launch_action'
/users/asadullahshafai/library/application support/sketchup 2019/sketchup/plugins/fredo6_roundcorner/bootstrap_roundcorner.rbe:81:in launch_action' /users/asadullahshafai/library/application support/sketchup 2019/sketchup/plugins/fredo6_roundcorner/bootstrap_roundcorner.rbe:96:in block in startup'
/users/asadullahshafai/library/application support/sketchup 2019/sketchup/plugins/fredo6_!libfredo6/lib6plugin.rbe:1407:in command_invoke' /users/asadullahshafai/library/application support/sketchup 2019/sketchup/plugins/fredo6_!libfredo6/lib6plugin.rbe:1388:in block (2 levels) in build_config_commands'
/users/asadullahshafai/library/application support/sketchup 2019/sketchup/plugins/fredo6_!libfredo6/lib6traductor.rbe:1378:in `block in add_command'