Pretty common as well (if not even more common, at least in the south): Skifahren.
How comes that K in Ski is not pronounced as usual (like in aktiv, Kompetenz, kaputt etc.)? Checked forvo.com and found the same pronunciation, which is something like shee. Also found that there is a German word, der Schi, which I understand why it is pronounced like shee. But Ski? Thanks.
I think that Ski is a loanword from Norwegian.
Wiktionary tells me ( https://en.wiktionary.org/wiki/ski#Norwegian_Bokm.C3.A5l ) that the word is pronounced /ʃiː/ in Norwegian, i.e. as if spelled Schi in German. So presumably the word was simply borrowed with its spelling and its pronunciation, even if the combination doesn't make sense from the point of view of German spelling rules.
A bit like English loanwords such as "valet" or "jalapeño", where the -t and j- aren't usually pronounced as in English.
That's already present as an option but is a fairly new one -- it may take a while for it to be accepted on the website, and possibly a bit longer still on the apps.
No; wrong word order. The adverb manchmal should be after the verb stem, and Ski at the end similar to a separable prefix.