Update from 6.5.0 to 6.5.2 language file nog working any more

-- HikaShop version -- : 6.5.2
-- Joomla version -- : 6.1.2
-- PHP version -- : 8.3

Hi Support,

After updating HikaShop from 6.5.0 to 6.5.2, the translations are no longer
loading anywhere in the back-end. Instead of the normal texts we now see the
raw language keys everywhere (for example SHOW_FOOTER, IMAGE_POPUP_MODE,
USE_CHOSEN, and even the update notice itself shows as
UPDATE_LANGUAGE / LOAD_LATEST_LANGUAGE). A screenshot is attached.

The important point: the Dutch language file is definitely present and
installed. We have verified this:

- In HikaShop > System > Configuration > Languages, Dutch (nl-NL) is listed
as installed. When we open it with the Edit icon, the full list of
translated strings is shown, so the file exists and is filled.
- Via FTP the file nl-NL.com_hikashop.ini is present and not empty, in both
/language/nl-NL/ and /administrator/language/nl-NL/.
- The files and folders have the correct read permissions.

What we have already tried, without any result:
- Reinstalled the HikaShop 6.5.2 package over the existing installation.
- Clicked "Load latest from server" for the Dutch language and saved.
- Cleared the Joomla cache.

So the nl-NL file is present, but HikaShop keeps showing the untranslated
keys after the update. Could you tell us what can cause the language file not
to be loaded, and how to solve it?