Hello, I have a problem with the site search on a German Website with the letters (ä; ü; ö; ß; –).
The German Word “Rücken” will change to “Rücken” or “Übungen” to “Ã�bungen”.
On the normal site (HTML) all is great, only in the site search (PHP).
Are there any setting options that I have overlooked?
Or do you have a good workaround without always write oe; ue; etc.?
Sparkle accounts for this, and it generally works fine. When it doesn’t work fine it’s in some cases an older PHP version running on the web server, or a Windows IIS web server that doesn’t have the necessary PHP module installed.
Hard to say without knowing the domain name and looking at the server.
Thank you for your fast answers! 
The Website is hosted by 1blu, a small German Hoster.
On the 1blu Website they say, that they support: PHP 7.4 / 7.3 / 7.2 / 7.1 / 5.6.
It’s currently running:
x-powered-by: PHP/5.3.29
So that’s the issue causing the incorrect characters.
Best upgrade to the latest version, 7.4.
For the Future, if someone else have the same problem with 1blu, here is the Link for the 1blu FAQ.