Here's a search on Google for my site.
Texts are different for each page of my site but snippets (meta description) are still the same for a Google search.
Can you give me an advice to change it?
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All your pages have same meta description like below.
From your source code, I just figure out all the pages have same meta description.
You're using Joomla. So in admin section global meta keywords and description takes if you are not set any description or meta data to individual pages.
So the solution is you have to set different meta data from you article section or menu sections in Joomla.