As I know, Laos is for country and Lao for people. Like England and English.

the only people I heard pronouncing the "s" on the end of "Laos" were someAmericans, who in my experience have a tendency to try to read any language according to their own phonetics conventions.....

I used to be highly amused by some of these attempts when taking US businessmen on trips around UK and Europe.

... Spent two weeks in northern Lao in September 2015, I was told by 3 expats from the USA, Britain & Australia who were running guest houses in different towns and were married to local girls from each a similar story that locals say they are Lao people who live in Lao and speak Lao ... When I protested that maps say Laos I was told that the French put the 's' on and the locals did not like it but they were much to polite to correct visitors ... That polite part I believe, don't know about the rest ... I found them to be a lovely sharing people with wonderful food, very low priced food, transport and accommodation, it's a beautiful safe country to visit. (well, safe apart from the mountain roads & old Chinese buses, but even those trips are a great experience)

When I was in Laos a few years ago I went off the beaten track, and came across a little village called llanfairpwllgwyngyllgogerychwyrndrobwllllantysilio gogogoch. Try as I could, I could work out whether the last two letters '...ch' were silent or not!

Why would you think that?

The country is Lao, the people are Lao. Laos is French.

Laos is now the English it would appear.

English pronunciation is with S sound. I have Lao language CDs and they say Laos with s when speaking English. It's like the French say Paree, English speakers say Paris. Also verified by Robert Cooper, who is fluent in Lao, has written 3 books on Laos, lives and owns a book store in Vientiene.

What you are forgetting is that Lao used to be a French colony and it is the French who added the "s".