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

Index: rtengine/rtthumbnail.cc
--- rtengine/rtthumbnail.cc.orig
+++ rtengine/rtthumbnail.cc
@@ -2204,7 +2204,7 @@ bool Thumbnail::readImage (const Glib::ustring& fname)
 
 bool Thumbnail::readData  (const Glib::ustring& fname)
 {
-    setlocale (LC_NUMERIC, "C"); // to set decimal point to "."
+    //setlocale (LC_NUMERIC, "C"); // to set decimal point to "."
     Glib::KeyFile keyFile;
 
     try {
