coalesce() -> coalesced

The code was already correct, but some of the text, and the value name
coalesceFun, still referenced a coalesce() function. (The toplevel
coalesce() was removed in ceylon/ceylon.language@50c2269.)
Add 'de' module for german version

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Add German translation of part 1
Add German translation of part 2
Add German translation of part 3