Twentyfifteen: How to disable /en (translation) and blog posts headerimages?

Twentyfifteen theme looks very good for my needs, but there is extra features that I don't need. How to disable them?

In url there is /en. I like to have simple urls like domain.com/blog/hello-world.
I tried disable all translation config in admin panel. Then I got errors.

Is there possible disable headerimages for blog posts? Theme decide add first image from posts to header.

I don't like to make custom theme for disable things. Why it isnt that way when you want to add things you make child theme?
Where is basic theme for basic people (skills to install and config in admin panel)?
Like a said twentyfifteen looks good for it but there is extra (for me).

(sorry bad english)

Should I make issue in Github?

Disable translation error debug:

grav.log

[2015-10-30 14:19:42] grav.CRITICAL: Call to a member function get() on a non-object - Trace: #0 .../twenty/vendor/filp/whoops/src/Whoops/Run.php(357): Whoops\Run->handleError(1, 'Call to a membe...', '.../userho...', 433) #1 [internal function]: Whoops\Run->handleShutdown() #2 {main} [] []

Screenshot

system.yaml

absolute_urls: false
param_sep: ':'
wrapped_site: false
languages:
  supported:
    - en
    - de
    - es
    - fr
    - it
    - nl 
    - el
    - pl
  include_default_lang: false
  translations: false
  translations_fallback: false
  session_store_active: false
  http_accept_language: false
  override_locale: false
  home_redirect:
    include_lang: true
    include_route: false
home:
  alias: /blog
pages:
  theme: twentyfifteen
  order:
    by: default
    dir: asc
  list:
---

If you remove all the supported translations, it will just default back to looking for default.md and URLs wont have the language codes in them. Read the docs on multilanguage for more information on what's going on there.