There is a unicode character known as a soft hyphen. The soft hyphen indicates where to break a word if it doesn't all fit on a line. This character should be used instead of a hard hyphen most of the time.
Too bad eBook readers are very inconsistent in their support for that. Some readers display an icon indicating an unknown glyph, many fail to insert the hyphen....
That soft hyphen would have been a blessing for the German e-books. Some texts are flush with the overly long words, making them very hard to read.
But Kindle (last time I checked) doesn't support it.
Neither the Calibre and few other e-book viewers/editors I have tried in the past.
In other words, in my experience the support is uniform and consistent: no support whatsoever, sadly.
P.S. On top of it, the Kindle devices I have, also have the rendering and text selection bugs when displaying/selecting the text around words (even if they are hyphenated) which are longer than the single visible line.