Currently, users trying to upload too large files get this error message:

Upload Failure:
PhabricatorFileUploadException:Uploaded file exceeds limit in Phabricator 'storage.upload-size-limit" configuration.

While this is a precise message for a sysadmin, it could be simpler and friendlier. For instance:

Upload Failure:
This file exceeds the limit of (size-limit).

Or something along these lines.

Original report: https://phabricator.wikimedia.org/T159