On iOS, the keyboard just suggests compounds. This works for those you use often. Another option is to choose a prefix, then backspace (over the space), then add to the prefix.

Example compound word: Schleifmaschinenverleih (word boundaries: Schleif'maschinen'verleih)

You begin with "Schl" which might suggest "Schleifer", then you delete "er", add "m", and if you're lucky, you get "Schleifmaschine".

"Schleifen" means to grind. "Maschine" means machine. So "Schleifmaschine" is grinding machine, and the disappearance of "en" is a grammatical artifact. "Verleih" means rental (as in a company that does rentals).

I just write the words separately and remove the spaces afterwards. An "I'm about to write a compound word"-button would be an easy solution, but it shouldn't be hard for the keyboard to automatically join the words after you've finished your sentence, it's mostly rule based.

There's the same problem in Swedish. I usually swipe the words separately or, if they're short, I type them manually and then go back to swiping. The decision to type them usually comes when I've tried a few times to swipe it before realising it's just not in the dictionary.

It's actually really frustrating. I absolutely love swiping, but it doesn't feel like it works very well with Swedish.

It just means phones ship with larger dictionaries.

And I would guess this isn't even the proper way to handle German. The long words are just sequences of words not split by spaces when writing. In a parallel universe the German writing system would use spaces and the language wouldn't need to change a bit.

Words are features of writing systems, not of languages.

I often just write separate words. Not correct, strictly speaking, but understandable.

I still prefer regular keyboards so (desktop and laptop) -- not sure if that's related.