Good Bye Lenin!
(2003)
BAFTA Nominee for Best Foreign Language Film

To protect his sick mother from a shock that might kill her, Alex goes to increasingly complex measures (including faking news broadcasts and hiding foreign foods) to ensure that she does not know that her beloved East Germany has reunified while she was in a coma.

The mother eventually finds out the truth before she falls ill again, but she doesn't tell her son, who creates one last broadcast - this time explaining that West Germans have flocked to East Germany to escape the tyranny of capitalism and that a new leader has been chosen (a taxi driver Alex paid).

She dies letting her son think he was successful.

 Thanks Mary C!