As more and more Nepalese people learn English which is part of most if not every school in the country, you will find that the Nepalese language is not an absolute necessity. On the other hand, I fully agree it would be nice to be able to speak the local language, and even better to be fluent in it. Foreigners who spend limited time in Nepal do not have to learn the language, why so? It is not a necessity. On the other hand it is clear that those who are planning to spend to live here as expats, or work with NGO's, or run a business or generally speaking intend to take an active part in the daily life and/or activities of the locals would do well to speak the language.
But this is where things get a bit more complex. I consider myself to be a very good linguist. I speak five languages, but not nepali! Let's face it, nepali is not an easy language to understand, and even harder for most (non-indian) foreigners to learn. According to Wikipedia, there is no one mother tongue in Nepal, there are 123 of them which they refer to as "mother tongue in Nepal". Most of them belong to the Indo-Aryan and sino-Tibetan language families. These nepalese languages are of course all based on Sanskrit, with ten diphthong sounds, six oral vowels and five nasal vowels. So without going into more detail, it starts to explain why so few foreigners among the people I know in Nepal speak the language. I can't even remember of single one among my friends who could write it!. Sanskrit is sanskrit, and obviously their writing bears no resemblance to ours in the west, be they europeans or north or south americans etc. with a totally different alphabet!
I tried to learn it when I was much younger and even spent good money on a teacher who came to my house to give me private lessons, but finally I had to capitulate! Others may find it easier, and I am the first one to admit I may have a hard skull; but whatever the reason was, that nepalese language just could not sink in!!
Others may find the nepali easier to learn..... and I hope they do.....at least try!
Imagine the value of knowing the language? being able to read and understand any undertaking, lease or other important paper such as court document etc in nepali language. No way the local people or any smartie can put one over on you! Best defense mechanism I know! In Nepal, believe me, knowing the language can be useful, particularly when a foreigner has interests at stake in that country. No longer have to rely completely on your lawyer...who in addition will never hesitate to charge you a lot of money per page.
Note: official translations in Nepal are not so well translated in english (or other) to be honest, and very costly. Ask any foreigner who has had to use official translators. It's a hassle.