Hi Welcome to Trip Advisor forum Nepal
As usual general people used to understand and speak Hindi and Urdu very well and not assume.Thank you.
I am not sure if Hindi and Urdu are similar, Hindi is widely understood in Nepal but I am not sure about Urdu. If you can Speak at least Hindi then it should be fine to explore around.
Many people in Kathmandu speaks good English; especially younger people and people working in hotels, restaurants, shops and tourist business etc.
So you will have no problems, I think :-)
First, you should know that very few visitors to Nepal bother to learn any Nepali. Even among longer term visitors the ability to speak Nepali not common because very few foreigners find themselves regularly in situations where they can't get by in English (or Hindi/Urdu).
To your question about whether people understand Hindi/Urdu, it depends a bit on who exactly you are interacting with. If they have a television, then they likely understand Hindi/Urdu (production values of Hindi media are generally higher than Nepali media). In Thamel and other tourist areas many people would understand both Hindi and English. If you are in Nepal primarily as a tourist in the major tourist areas, then you are most likely to be primarily interacting with people who have a lot of contact with tourists (both western and Indian) and would be very likely to understand both hindi and english and you would definitely be able to get by without a problem. If you are going beyond the traditional tourist areas of Kathmandu, people with more media exposure often understand Hindi but may not be able to speak it (can also apply to some taxi drivers).
One last thing to be a bit aware of is that not everyone in Nepal appreciates being spoken to in Hindi. Relations between India and Nepal are...complicated. You may actually be better off starting in English and if you need to fall back to Hindi, apologize for not knowing Nepali.
But the short answer is you'll be fine.
Thanks for all of the replies! Urdu and Hindi are close enough, like British and American English. I was planning to visit areas near Boudhanath, but I imagine I would go to other areas of the city as well. I actually wasn't planning to go to Thamel though (too crowded from what I have read, trying to go to more open/less tourist crowded areas)
If you can then it's always good to speak English. As said on ## Post 04 / second last paragraph Nepali people do not fully enjoy talking in Hindi so it's good to practice English. People speak basic English common.
I would think there would be more people speaking rudimentary Hindi than English in Nepal, even in Kathmandu. People in the tourist business do speak some English but the "man on the street" does not. So if you plan to communicate with the natives outside the touristy places knowing Hindi would certainly be helpful.
all people can speck hindi