TBH, out of context "Rechner" means calculator.
No.
"Rechner" means computer.
Calculator is called "Taschenrechner" (translated word by word: pocket computer).
Never heard anyone shortening "Taschenrechner" to just "Rechner".
Neither have I, but I'd hesitate to lecture a fellow Germanophone (cybersmurf is Austrian) about our shared mother-tongue.
As to Computer and Calculator: I struggle to remember what the difference even is - the explanation of
this site here seems dubious (I doubt that anyone used electronic calculators before the 20th century, and the main functional difference they cite appears to be akin to parallel vs. sequential operation). IIRC 'computer' was once a bona-fide job performed by humans. Persistent human errors lead to the invention of Babbage's Difference engine via a requirement by the Royal Navy, methinks - after a RN Destroyer was shipwrecked due to a tiny error in a logarithm table complied by humans.
it gets weird if foreign words get Germanized and bent to German grammar.
I wonder how often English bastardises words like that.
According to my former boss, this
is actually a thing in English, too - as well as being a bona-fide research-subject in linguistics (His wife is also a professor at the local Uni, and the resident star-linguist). IIRC, he cited an example that originated with American Football-jargon, where a neologism used by football fans became widely used - but strikingly, the usage of the neologism followed grammar-rules that the original root-word did not.
Afrikaans follows the same logic, and has rekenaar and sakrekenaar for computer and calculator.
Do you understand spoken Afrikaans? My Dutch is
very rusty, but I can usually follow the gist of a Dutch conversation - not so with Afrikaans.