Why language specific params defined in "[lanuage]" missing some information defined outside "[lanuage]"

[params]
    [params.home]
        var1 ="1"
        var2 ="2"

[languages]
    [languages.en]
        [languages.en.params.home]
            var1="changed"

The language specific params will override the variable with the same name defined outside of "[language]",
In above example, there is no var2 availble, and Site.Params.Home only can see var1="changed"

Why baseURL defined in config file doesn’t take effect when running in hugo server mode?

All the baseURL will with baseUrl "http://localhost:port" when run in hugo server mode,
but if you run hugo command, you can see the baseUrl you specified contains in geneated pages.
the workaround is run hugo server -b [baseURL] to explicitly specify the baseURL

How to list all the pages under specific subdir without using taxonomy?

There is no easy way to do that, especially if you want to paginator the pages.
I wrote a document to detail desribe how to do it here:
Hugo list all the pages under sub directories