RightToLeft

RightToLeft seems to be a enum and your GetObject is returning a string, so you should try using enum.parse which will convert the string representation of the name or numeric value of one or more enumerated constants to an equivalent enumerated object

 this.RightToLeft = (RightToLeft)Enum.Parse(typeof(RightToLeft), rmLanguage.GetString("frmUsersConfig.RightToLeft"));

If you want to know more about enum.parse, you can check out the msdn link

http://msdn.microsoft.com/en-us/library/essfb559.aspx