Description of problem:
This is related to RFE bug 1623128 (modulemd fail-safe cache) which was not completely enabled, however the code is mostly in and just hard Errors were changed to Warnings. However, the warning itself is quite unfortunate (see output below) at least due to 2 reasons:
a) messages are not identified as Warnings and thus are very likely to be missed
b) dnf says for the package "it cannot be installed on the system" while it IS installed.. this confusing part should be changed/removed.
# dnf -y update
No available modular metadata for modular package 'TestC-1-1.modC.noarch', it cannot be installed on the system <---
No available modular metadata for modular package <---
Preparing : 1/1
Upgrading : TestC-1-1.modC.noarch 1/2
Cleanup : TestC-0.1-1.noarch 2/2
Verifying : TestC-1-1.modC.noarch 1/2
Verifying : TestC-0.1-1.noarch 2/2
Installed products updated.
Version-Release number of selected component (if applicable):
I create a commit that change two strings: https://github.com/rpm-software-management/dnf/pull/1429/commits/5b3fb077592a4c3f7cadcc1b3c3476b4448c7d3b
The new strings are now uploaded to Zanata and ready for translation.
This bug report is not relevant anymore because the original bug https://bugzilla.redhat.com/show_bug.cgi?id=1623128 was fully resolved and the warning is not in the code.