WIP/RFC: add locale folder for `helpdb.jl`

If `sys.ji` in https://github.com/JuliaLang/julia/issues/2498 can be alted,
this pull would create a `help` folder in `$(BUILD)/share/julia/help/`
and `LOCALE` for `base/util.jl` to eval specific `helpdb_what_ever_lang.jl`