Index: ps/trunk/source/scriptinterface/ScriptConversions.cpp
===================================================================
--- ps/trunk/source/scriptinterface/ScriptConversions.cpp
+++ ps/trunk/source/scriptinterface/ScriptConversions.cpp
@@ -158,16 +158,10 @@
 
 template<> bool ScriptInterface::FromJSVal<std::string>(JSContext* cx, JS::HandleValue v, std::string& out)
 {
-	JSAutoRequest rq(cx);
-	WARN_IF_NOT(v.isString() || v.isNumber(), v); // allow implicit number conversions
-	JS::RootedString str(cx, JS::ToString(cx, v));
-	if (!str)
-		FAIL("Argument must be convertible to a string");
-	char* ch = JS_EncodeString(cx, str); // chops off high byte of each char16_t
-	if (!ch)
-		FAIL("JS_EncodeString failed"); // out of memory
-	out.assign(ch, ch + JS_GetStringLength(str));
-	JS_free(cx, ch);
+	std::wstring wideout;
+	if (!FromJSVal(cx, v, wideout))
+		return false;
+	out = CStrW(wideout).ToUTF8();
 	return true;
 }
 
@@ -265,12 +259,7 @@
 
 template<> void ScriptInterface::ToJSVal<std::string>(JSContext* cx, JS::MutableHandleValue ret, const std::string& val)
 {
-	JSAutoRequest rq(cx);
-	JS::RootedString str(cx, JS_NewStringCopyN(cx, val.c_str(), val.length()));
-	if (str)
-		ret.setString(str);
-	else
-		ret.setUndefined();
+	ToJSVal(cx, ret, static_cast<const std::wstring>(CStr(val).FromUTF8()));
 }
 
 template<> void ScriptInterface::ToJSVal<const wchar_t*>(JSContext* cx, JS::MutableHandleValue ret, const wchar_t* const& val)
Index: ps/trunk/source/scriptinterface/tests/test_ScriptConversions.h
===================================================================
--- ps/trunk/source/scriptinterface/tests/test_ScriptConversions.h
+++ ps/trunk/source/scriptinterface/tests/test_ScriptConversions.h
@@ -1,4 +1,4 @@
-/* Copyright (C) 2019 Wildfire Games.
+/* Copyright (C) 2020 Wildfire Games.
  * This file is part of 0 A.D.
  *
  * 0 A.D. is free software: you can redistribute it and/or modify
@@ -148,9 +148,9 @@
 
 		roundtrip<std::string>("", "\"\"");
 		roundtrip<std::string>("test", "\"test\"");
-		roundtrip<std::string>("тест", "\"\\xD1\\x82\\xD0\\xB5\\xD1\\x81\\xD1\\x82\"");
+		roundtrip<std::string>("тест", "\"\\u0442\\u0435\\u0441\\u0442\"");
 		roundtrip<std::string>(s1, "\"t\\x00st\"");
-		roundtrip<std::string>(s2, "\"\\xD1\\x82\\x00\\x00\\xD1\\x81\\xD1\\x82\"");
+		roundtrip<std::string>(s2, "\"\\u0442\\x00\\x00\\u0441\\u0442\"");
 
 		roundtrip<std::wstring>(L"", "\"\"");
 		roundtrip<std::wstring>(L"test", "\"test\"");
@@ -251,4 +251,28 @@
 		CFixedVector3D u(fixed::Pi(), fixed::Zero(), fixed::FromInt(2));
 		call_prototype_function<CFixedVector3D>(u, v, "add", "({x:3.1415863037109375, y:3.1415863037109375, z:3})");
 	}
+
+	void test_utf8utf16_conversion()
+	{
+		// Fancier conversion: we store UTF8 and get UTF16 and vice-versa
+		ScriptInterface script("Test", "Test", g_ScriptRuntime);
+		TS_ASSERT(script.LoadGlobalScripts());
+		JSContext* cx = script.GetContext();
+		JSAutoRequest rq(cx);
+
+		std::string in_utf8("éè!§$-aezi134900°°©©¢¢ÇÇ‘{¶«¡Ç’[å»ÛÁØ");
+		std::wstring in_utf16(L"éè!§$-aezi134900°°©©¢¢ÇÇ‘{¶«¡Ç’[å»ÛÁØ");
+
+		JS::RootedValue v1(cx);
+		ScriptInterface::ToJSVal(cx, &v1, in_utf8);
+		std::wstring test_out_utf16;
+		TS_ASSERT(ScriptInterface::FromJSVal(cx, v1, test_out_utf16));
+		TS_ASSERT_EQUALS(test_out_utf16, in_utf16);
+
+		JS::RootedValue v2(cx);
+		ScriptInterface::ToJSVal(cx, &v2, in_utf16);
+		std::string test_out_utf8;
+		TS_ASSERT(ScriptInterface::FromJSVal(cx, v2, test_out_utf8));
+		TS_ASSERT_EQUALS(test_out_utf8, in_utf8);
+	}
 };