Logic Masters Deutschland e.V.

Notice: This is a Sudoku puzzle I made for CCBC15 (a Chinese Puzzle Hunt, which has now ended), so Solution code is an English word or vocabulary.

Standard Sudoku rules apply.
Each row, column, and region indicated by thick borders in the grid must contain the digits 1 to 9 once each.

Little Killer rules apply.
The numbers on the diagonal are the sum of all the numbers on that diagonal.

Dutch Whisper Line rules apply.
Digits along each Dutch Whisper Line (orange) must differ by at least four(4).

German Whisper Line rules apply.
Digits along each German Whisper Line (green) must differ by at least five(5).

Skyscrapers rules apply.
TNumbers in the grid represent the heights of skyscrapers, and clues outside the grid indicate the number of skyscrapers visible in that row or column, looking in that direction.

Play this puzzle on SudokuPad.

即便是不同国家的低语，也能构建起璀璨的高楼。

Hint: How to extract
Notice the river shaped areas? You need to convert the numbers in each row of the region to letters by adding them separately.

A simpler version of that sudoku was also provided in the original tip, but I don't know how to make the hidden picture, so I won't provide it here.