How to translate the search block title? In Drupal 8.1.1 I am able to translate customs block and basic blocks (block type).

The search block seems not to be translatable. But I need to translate the title of the standard search block. I can not find a way to do it. Words like "Search" are translated in all languages but the search block title gets not translated.
This is configuration translation. You have to enable the module with this name and then go to block layout, configure a block and click on the tab "Translate block":

/admin/structure/block/manage/mytheme_search/translate