How could I check that in my browser?
It isn't your browser that matters; it is the locale that was used when the webpage you're viewing was created.
So what to do now?
Ask the person who created your website what locale they used.
Nobody created my site.
In folder that I try to access there is only .htaccess file and index.php file:
<html><body><h1>It works!</h1>
<p>This is the default web page for this server.</p>
<p>The web server software is running but no content has been added, yet.</p>
</body></html>
Any idea?