diff --git a/doc/classes/OS.xml b/doc/classes/OS.xml
index 26110df3356..a2ec342c81b 100644
--- a/doc/classes/OS.xml
+++ b/doc/classes/OS.xml
@@ -201,7 +201,12 @@
 			<return type="String">
 			</return>
 			<description>
-				Returns the host OS locale.
+				Returns the host OS locale as a string of the form [code]language_Script_COUNTRY_VARIANT@extra[/code].
+				[code]language[/code] - 2 or 3 letter [url=https://en.wikipedia.org/wiki/List_of_ISO_639-1_codes]language code[/url], in lower case.
+				[code]Script[/code] - optional, 4 letter [url=https://en.wikipedia.org/wiki/ISO_15924]script code[/url], in title case.
+				[code]COUNTRY[/code] - optional, 2 or 3 letter [url=https://en.wikipedia.org/wiki/ISO_3166-1]country code[/url], in upper case.
+				[code]VARIANT[/code] - optional, language variant, region and sort order. Variant can have any number of underscored key words.
+				[code]extra[/code] - optional, semicolon separated list of additional key words. Currency, calendar, sort order and numbering system information.
 			</description>
 		</method>
 		<method name="get_model_name" qualifiers="const">
diff --git a/platform/osx/os_osx.mm b/platform/osx/os_osx.mm
index c4eb5407af0..c07e6344894 100644
--- a/platform/osx/os_osx.mm
+++ b/platform/osx/os_osx.mm
@@ -284,7 +284,7 @@ Error OS_OSX::shell_open(String p_uri) {
 
 String OS_OSX::get_locale() const {
 	NSString *locale_code = [[NSLocale preferredLanguages] objectAtIndex:0];
-	return [locale_code UTF8String];
+	return String([locale_code UTF8String]).replace("-", "_");
 }
 
 String OS_OSX::get_executable_path() const {
diff --git a/platform/windows/os_windows.cpp b/platform/windows/os_windows.cpp
index 5b15896b0c9..a3e23a9053e 100644
--- a/platform/windows/os_windows.cpp
+++ b/platform/windows/os_windows.cpp
@@ -567,21 +567,21 @@ String OS_Windows::get_locale() const {
 
 	LANGID langid = GetUserDefaultUILanguage();
 	String neutral;
-	int lang = langid & ((1 << 9) - 1);
-	int sublang = langid & ~((1 << 9) - 1);
+	int lang = PRIMARYLANGID(langid);
+	int sublang = SUBLANGID(langid);
 
 	while (wl->locale) {
 		if (wl->main_lang == lang && wl->sublang == SUBLANG_NEUTRAL)
 			neutral = wl->locale;
 
 		if (lang == wl->main_lang && sublang == wl->sublang)
-			return wl->locale;
+			return String(wl->locale).replace("-", "_");
 
 		wl++;
 	}
 
 	if (neutral != "")
-		return neutral;
+		return String(neutral).replace("-", "_");
 
 	return "en";
 }