Well, the UI portion is fairly straight foward but you'd need to follow the rules for syntax and grammar of the chosen language which can get quite complicated. I know Tolkien covered some of his languages in depth while others he glossed over so finding correct rules might be the most difficult part of your project.
In terms of getting started writing Lua plugins, I might be a bit biased but I'd recommend the
Writing LoTRO Lua Plugins for Noobs thread on the Turbine forums.