I'm still learning.
This is what I put in that file just in case you may need to update the future version.
//Vietnamese
'À'=>'a','Á'=>'a','Ả'=>'a','Ã'=>'a','Ạ'=>'a','à'=>'a','á'=>'a','ả'=>'a','ã'=>'a','ạ'=>'a',
'Ă'=>'a','ă'>'a','Â'=>'a','â'=>'a',
'Ằ'=>'a','Ắ'=>'a','Ẳ'=>'a','Ẵ'=>'a','Ặ'=>'a','ằ'=>'a','ắ'=>'a','ẳ'=>'a','ẵ'=>'a','ặ'=>'a',
'Ầ'=>'a','Ấ'=>'a','Ẩ'=>'a','Ẫ'=>'a','Ậ'=>'a','ầ'=>'a','ấ'=>'a','ẩ'=>'a','ẫ'=>'a','ậ'=>'a',
'Đ'=>'d','đ'=>'d',
'È'=>'e','É'=>'e','Ẻ'=>'e','Ẽ'=>'e','Ẹ'=>'e','è'=>'e','é'=>'e','ẻ'=>'e','ẽ'=>'e','ẹ'=>'e',
'Ê'=>'e','ê'=>'e',
'Ề'=>'e','Ế'=>'e','Ể'=>'e','Ể'=>'e','Ệ'=>'e','ề'=>'e','Ế'=>'e','Ể'=>'e','Ễ'=>'e','Ệ'=>'e',
'Ì'=>'i','Í'=>'i','Ì'=>'i','Ĩ'=>'i','Ị'=>'i','ì'=>'i','í'=>'i','ỉ'=>'i','ĩ'=>'i','ị'=>'i',
'Ô'=>'o','ô'=>'o','Ơ'=>'o','ơ'=>'o',
'Ồ'=>'o','Ố'=>'o','Ổ'=>'o','Ỗ'=>'o','Ộ'=>'o','ồ'=>'o','ố'=>'o','ổ'=>'o','ỗ'=>'o','ộ'=>'o',
'Ờ'=>'o','Ớ'=>'o','Ở'=>'o','Ỡ'=>'o','Ợ'=>'o','ờ'=>'o','ớ'=>'o','ở'=>'o','ỡ'=>'o','ợ'=>'o',
'Ư'=>'u','ư'=>'u',
'Ừ'=>'u','Ứ'=>'u','Ử'=>'u','Ữ'=>'u','Ự'=>'u','ừ'=>'u','ứ'=>'u','ử'=>'u','ữ'=>'u','ự'=>'u',
'Ỳ'=>'y','Ý'=>'y','Ỷ'=>'y','Ỹ'=>'y','Ỵ'=>'y','ỳ'=>'y','ý'=>'y','ỷ'=>'y','ỹ'=>'y','ỵ'=>'y',