Hello Trevor, thank you for your reply.

There’s only one type of posts included in the search and none of them are translated, as of yet, in other languages than the standard language (Dutch).
I’ll try to describe the exact problem (all in the standard language):
– when Polylang is not yet activated, loading the page with all the (pre-filtered) posts and filtering the results works fine (the message ‘No results found’ is <u>not</u> displayed, only the correct filtered results)
– when Polylang is activated, loading the same page with the posts works, but filtering the results (using any of the four filters) immediately returns the message ‘No results found’
– when I deactivate ‘Loading results using Ajax’, the filtering works again (with Polylang still active)
This led me to the conclusion that there’s a possible conflict between Polylang and the use of Ajax in the filter. But I could be wrong (I’m not a programmer).
Point is that the client would like to see the smooth transition when filtering with Ajax, not the abrupt reloading when Ajax is deactivated.
Is this information enough to look into this problem?

Kind regards,
Jef