First of all - nice plugin, it has a real good potential ..
I am a bit confused though, you have authored ( at least )two very similar plugins,
one is " Ultimate WP Query Search Filter " and the other is "Advance WP Query Search Filter" ..
On the later ( "Advance.." ) the plugin presentation page states
his plugin is an upgraded version of WP_Query Search Filter...But clearly The plugin ( "Ultimate.." ) was updated more recently ..
So which version is the one maintained and developed ? Both?
On the same argument - I would like to help contributing some code improvements that I have made ( especially i18l, Translations, RTL support and non-english characters support ) . .where and how can I do such a thing ? Do you have a bitbucket / github page ?