By default the search should only display the results in the currently active language on the front-end. I have double checked if there is any issue there, but it works fine on my local (and online) test environments. I couldn't find any similar tickets from the past couple of weeks, so this might be something new.
There are a few things you should check:
– That if the WPML compatibility is indeed enabled: https://i.imgur.com/clmyEgR.png
– If the custom ajax handler is enabled, try disabling it: https://i.imgur.com/csmcteT.png
If those are okay, but no change, then one other thing you could try is to switch to the index table engine. It explicitly stores the language code along with the keywords, so it might do the trick.
Unfortunately I'm not sure I'm able to tell what exactly the problem might be, unless I can test it somehow. If none of these suggestions work, and you can arrange some sort of online test environment that I can access, please let me know.Best,
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