Apply character encoding conversion to hard-coded strings

This fixes an issue where menu items like "戻る" were garbled in Unicode
mode.

src/sys/nact_sys3.cpp

@@ -265,7 +265,7 @@ void NACT_Sys3::cmd_open_obj(int verb)
 	// 戻るを追加
 	ags->menu_dest_x = 2;
 	ags->menu_dest_y += 2;
-	ags->draw_text(strings::back[lang]);
+	ags->draw_text(strings.back);
 	id[index++] = 0;
 	ags->menu_dest_y += ags->menu_font_size + 2;
 	ags->draw_menu = false;