diff --git a/screen_ui.cpp b/screen_ui.cpp
index 9198073..2a8d7f9 100644
--- a/screen_ui.cpp
+++ b/screen_ui.cpp
@@ -1099,9 +1099,9 @@
   rtl_locale_ = false;
 
   if (!new_locale.empty()) {
-    size_t underscore = new_locale.find('_');
-    // lang has the language prefix prior to '_', or full string if '_' doesn't exist.
-    std::string lang = new_locale.substr(0, underscore);
+    size_t separator = new_locale.find('-');
+    // lang has the language prefix prior to the separator, or full string if none exists.
+    std::string lang = new_locale.substr(0, separator);
 
     // A bit cheesy: keep an explicit list of supported RTL languages.
     if (lang == "ar" ||  // Arabic