As far as I know, I've never been to Kathmandu, most of people in Kathmandu speak
Nepali and dialect.(Maithili, Nepal Bhasa, Bhojpuri, Tharu, Gurung, Tamang, Magar, Awadhi, Sherpa, Kiranti and another 100 different indigenous languages.)
Nepali is an Indo-Aryan language spoken in Nepal, Bhutan, and some parts of India and Myanmar (Burma).
Another issue is
Air pollution; it is a problem in Kathmandu which human health is severely affected. The pollution in Kathmandu is mainly due to vehicular emission, poor quality rood, fuel etc.
You can check the information from
http://www.most.gov.np/pollution/pollution.php
There are some studies state that the linkages between meteorological processes and air pollution in the lower atmosphere of the Kathmandu Valley. The physical setting of Kathmandu also influences air pollution concentrations.
Visit Kathmandu's official Website
http://www.kathmandu.gov.np/