We face the same issue in nopcommerce 4.2 when trying nopajaxfter pro trial version. We have two languages English and Arabic. But in Arabic the drop down list for categories and manufacturers still get the English values.
Everything is working properly on our demo store.
You can see that we have the Books category named Books RTL and the HTC manufacturer names HTC RTL in the English RTL language and they are properly loaded in the Ajax Filters Pro on our demo store when you change the language to English RTL.http://demos.nop-templates.com/