501(c)3 organizations can engage in lobbying as long as it does not constitute a substancial portion of the organization's activity. 501(c)3 organizations have an absolute ban on lobbying for candidates for public office, however.
This would not threaten Wikipedia's tax-exempt status.
The WM produces one project: Wikipedia, the bulk of which is the English-language version. If that is given over entirely to lobbying a specific bill, even temporarily, they would have a very hard time arguing that that is not a "substantial portion" of their activity.
"Substantial portion" from the IRS perspective would involve money or staff time. They have 2 floors of staff. None of whom need be involved in this other than possibly to approve the release of some community-requested code changes.
This would not threaten Wikipedia's tax-exempt status.