First of all, I would like you to remember that I am not expert in Limbu language. I am a leaner. I am trying to learn Limbu language. I am sharing you whatever I have learned through this blog (in series). I cannot answer all your questions relating to Limbu language but I will always try to. If you do not get the answer then you should understand that I am not capable of answering it.
Limbu language is one of the languages of Tabeto-Burman language family. Limbu is spoken in Eastern part of Nepal (east from Arun river) which is known as Limbuwan, Darjeeling and Sikkim in India and Bhutan. Limbu language has four dialects. They are Phedape, Panchthare, Chhathare and Tamar Khole. Panchthare is the standard dialect of Limbu language which is for the for educational, print and broadcasting Panchthare is used as Limbu language.
Limbu community is based on oral tradition. It does not have long history of written tradition. However, it has it’s own script and phonetic symbols for writing. Limbu script is known as Kirat Sirijong script. Kirat king Sirijong introduced Kirat Sirijonga script in 9th century. It was promoted later in 18th century by Te-Ongsi Sirijonga Thebe. He was sentenced to death for promoting Limbu language in Sikkim. Limbu community remembers him as martyr. Nepal government published a postal stamp to recognize his contribution to Limbu language.
I think learning script or letters is the first phase of learning language because we have already entered into the written tradition. You can use this photo to learn to write. This is the first step.
Good Luck !