https://github.com/Beep6581/RawTherapee/issues/6452

Index: rtgui/options.cc
--- rtgui/options.cc.orig
+++ rtgui/options.cc
@@ -741,7 +741,7 @@ void Options::filterOutParsedExtensions()
 
 void Options::readFromFile(Glib::ustring fname)
 {
-    setlocale(LC_NUMERIC, "C");  // to set decimal point to "."
+    //setlocale(LC_NUMERIC, "C");  // to set decimal point to "."
 
     Glib::KeyFile keyFile;
 
