Definition of independent for the purposes of this question: source is not owned by a for-profit corporation, is not financially backed by any billionaire (either directly or via foundation or nonprofit organization) and is not financed by any national government (even if run without oversight).
It can have any perceived bias or political leaning.
Edit: Just to add it has to be written in English.
Propublica
From their about page:
ProPublica is an independent, nonprofit newsroom that produces investigative journalism with moral force. We dig deep into important issues, shining a light on abuses of power and betrayals of public trust — and we stick with those issues as long as it takes to hold power to account.
With a team of more than 150 dedicated journalists, ProPublica covers a range of topics including government and politics, business, criminal justice, the environment, education, health care, immigration, and technology. We focus on stories with the potential to spur real-world impact. Among other positive changes, our reporting has contributed to the passage of new laws; reversals of harmful policies and practices; and accountability for leaders at local, state and national levels.
Investigative journalism requires a great deal of time and resources, and many newsrooms can no longer afford to take on this kind of deep-dive reporting. As a nonprofit, ProPublica’s work is powered primarily through donations. The vast bulk of the money we spend goes directly into world-class, award-winning journalism. We are committed to uncovering the truth, no matter how long it takes or how much it costs, and we practice transparent financial reporting so donors know how their dollars are spent.
ProPublica was founded in 2007–2008 with the belief that investigative journalism is critical to our democracy. Our staff remains dedicated to carrying forward the important work of exposing corruption, informing the public about complex issues, and using the power of investigative journalism to spur reform.