I want to know whether a place is wheelchair-accesible or not.
Data for the whole world is best, but data for specific countries/cities is OK too.
Data must be reusable in Wikivoyage, which is Creative Commons Attribution-ShareAlike 3.0 licensed.
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NPR has been developing a crowdsourced database of accessible playgrounds in the US. The data is downloadable as CSV or JSON. The license for the data isn't clearly stated, but the language suggests that they want it to be freely used.
There is WheelMap, a map based on OpenStreetMap which highlights wheelchair-accessibility tags. There is also supposedly Rollstuhlkarte but it doesn't seem to be actually showing any wheelchair symbols.
I know this is late, but: You might want to consider using accessibility.cloud. It provides a standardized way to access place accessibility data over multiple datasets, including the data from wheelmap.org, and others.